I_C4_Alkenes and other compounds containing C=C double bonds.pdf

7/21/2019 I_C4_Alkenes and other compounds containing C=C double bonds.pdf

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C H A P T E R

4

A l k e n e s a n d O t h e r C o m p o u n d s

C o n t a i n i n g C .... C D o u b l e B o n d s

In-Plane Vibratio ns 56

Out-of-Plane Vibration s 56

Band Absorbance Ra t ios and Frequency Separa t ions for Vinyl Twis t , Vinyl

C----CH2, an d Vin yl CH----CH2 W ag 57

Raman Da ta for X-CH-- --CH2 Com pou nds 58

C o n ju g a t e d V in yl G r o u p s 5 8

Rota t iona l Confo rmers or Fe rmi Resonance (ER.) 58

1-Alkene (CH= CH 2) CH and CH2 S t re tch ing Vibra t ions 60

C=C H2 Wag Frequenc ies vs ( s igma r~-sigma ) 60

CH----CH2 Twist Frequencies vs o 1 a n d p K a o f G f o r G - C H 2 C O 2 H 6 0

Allyl Halides 61

Cyc loa lkenes and Cyc loa lkadienes 61

Alkyl Acryla te s and Alkyl Methac ry la te s 62

Trans-Alkenes 63

Alkylc innamates 64

Cinnam yl Es te r s 65

1,1-Disubs t i tu ted Ethylenes 64

Styrenes and a -Methyl S tyrenes 65

Butadienes , P ropadienes , Conjug a ted Cyc l ic Dienes 66

Alkyl Group s of 1-Alkenes and Vinyl Alkyl Ethe r s 67

Refe rences 67

Figures

Figure 4-1 68 (61) Figure 4-4 70 (65)

Figure 4-2 69 (64) Figure 4-5 71 (65)

Figure 4-3 70 (65)

Tables

Table 4-1 72 (56, 57) Table 4-5 78 (61)

Table 4-2 73 (56) Table 4-5a 78 (62)


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56

Alkenes and O ther Compounds

C o n t a in i n g C = C

Double Bonds

Tables

Table 4-11 84 (64)

Table 4-11a 85 (64)

Table 4-12 85 (65)

Table 4-13 86 (65)

Table 4-14 87 (65)

Table 4-15 88 (65)

Table 4-16 89

Table 4-17 90

Table 4-18 91

*Numbers in parentheses indicate in- text page reference.

T h e I R sp ec t r a o f a v a r i e ty o f ch em ica l s co n ta in in g ca r b o n - c a r b o n d o u b le b o n d s ( C = C )

to g e th e r w i th sp ec t r a - s t r u c tu r e co r r e l a t io n s a r e r ead i ly av a i l ab l e i n b o o k f o r m to a id ch em is t s i n

th e id en ti f i c a tio n o f t h e se im p o r t an t p o ly m er b u i ld in g b lo ck s ( 1 ). C h ap te r 4 co n ta in s I R an d

Ram an d a t a f o r t h e se co m p o u n d s in di f f er en t en v i r o n m en t s . D i scu ss io n s o f b o th c h em ica l an d

p h y s i ca l e f f ec t s u p o n g r o u p f r eq u en c ie s a s so c i a t ed wi th ca r b o n - ca r b o n d o u b le b o n d s a r e

inc luded .

T ab le 4 .1 l i s t s v ib r a t io n a l a s s ig n m en t s f o r C= C s t r e t ch in g ( v C= C) , v in y l tw i s t , v in y l CH2

wag , v in y l CH= CH 2 w ag , an d th e f i r st o v e r to n e o f v in y l CH2 wag in t h e v ap o r - p h ase ( 2 ). T h e

v C - - C m o d e f or 1 - a lk e ne s ( R - C H - - C H 2 ) o c c u r in t h e re g i o n 1 6 4 1 - 1 6 5 0 c m - 1 . T h e v i n y l t w i s t

m o d e o ccu r s i n t h e r eg io n 9 9 1 - 1 0 0 8 cm - 1 . Br an ch in g in t h e 3 - ca r b o n a to m in c r ea se s t h e v in y l

tw i s t f req u ency . T h e v in y l C = C H2 wag o ccu r s i n t h e r eg io n 9 1 0 - 9 1 8 cm - 1 an d i ts f i rs t o v e r to n e

o ccu r s i n t h e reg io n 1 8 2 9 - 1 8 3 5 c m - 1 . T h e v in y l wag v ib r a t io n o ccu r s i n t h e r eg io n 5 7 2 -

6 8 5 cm - 1 . T h i s v ib r a t io n in c r ea se s i n f r eq u en cy wi th in c r ea sed su b s t i t u t io n o n th e 3 - ca r b o n

a to m (e .g ., R - C H 2 - C H = C H 2 , 5 7 2 - 6 2 7 c m - 1 ; R 2 C H - C H = C H 2 , 6 5 3 - 6 7 8 c m - 1, a n d

R 3 C - C H = C H 2 , 6 8 1 - 6 8 5 c m - 1 ).

Ab so r b an ce r a t io s an d f r eq u en cy sep a r a t io n s a r e a l so p r e sen ted f o r so m e v ib r a t io n a l b an d s .

I N - P L A N E V I B R A T I O N S

T ab le 4 .2 l i st s IR v ap o r - p h ase f r eq u en c ie s an d a ss ig n m en t s f o r a v a r i e ty o f co m p o u n d s co n ta in -

in g C= C d o u b le b o n d s . A c r y lo n i t ri l e an d d iv in y l su lf o n e ex h ib i t v C= C a t 1 6 1 3 an d 1 6 2 0 cm - 1 ,

r e sp ec tiv ely . T h e a l ly l d e r iv a tiv e s ex h ib i t v C - - C in t h e r eg io n 1 6 4 1 - 1 6 5 3 cm - 1 . I t is ap p a r en t

th a t CN an d SO2 g r o u p s jo in ed to t h e v in y l g r o u p h av e th e e f fec t o f l o wer in g th e C = C s t r e t ch in g

f requency (3) .

T h e v a sy m . CH2 = , v sy m . CH2 = , an d CH2 - - b en d in g m o d es o ccu r i n t h e r eg io n s 3 0 8 2 - 3 1 2 2 ,

2 9 9 5 - 3 0 4 5 , an d 1 3 8 9 - 1 4 3 0 cm - 1 , r esp ec tiv e ly . T h e C N an d SO2 g r o u p s r a i se t h e v a sy m . CH 2 =

f r eq uen c ie s . Co m p ar e ac r y lo n i tr i l e ( 3 1 2 2 cm - 1 ) an d d iv in y l su l f o n e ( 3 1 1 0 cm - 1 ) v s t h o se f o r 3-

b u ten o ic ac id an d th e a l l yl d e r iv a t iv e s ( 3 0 8 2 - 3 1 0 0 cm - 1 ) .


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Variables in Data Interpretation 57

jo ined to the su l fur a tom of the SO2 group . Al l o f the o ther compounds exhib i t CH--CH2 twis t in

t h e reg i o n 9 7 0 -9 9 7

c m - 1 ,

and in these cases the v iny l g roup i s jo ined to a carbon a tom .

Th e C=CH2 wag v ib ra t i o n an d i t s f i r s t o v e r t o n e o ccu r i n t h e reg i o n s 9 1 1 -9 7 1

c m - 1

an d

1 8 3 5 - 1 9 4 2 c m - 1 , respect ive ly . The CN and SO2 groups cause the C=CH2 wag mode to occur a t

h ig h e r f req u en cy t h an t h e o th e r v in yl co mp o u n d s , wh i ch exh i b i t t hi s mo lecu l a r v i b ra ti o n i n t h e

reg i o n 9 1 1 -9 3 4

c m - 1 .

As n o t ed h e re , t h e CH=CH2 wag mo d e fo r v in y l g ro u p s j o in ed t o R-CH2 , (R- )2 CH, an d

R- 3 C g ro u p s fo r 1 -a lk en es o ccu r in t h e reg i o n s 5 7 2 -6 2 7 , 6 5 3 -6 7 8 , an d 6 8 1 -6 8 5 cm -1 ,

re sp ec ti v ely. Wi t h t h e excep t i o n s o f al ly l fo rma t e (6 3 8 cm -1 ) , a ll y l b en zen e (6 4 8 cm -1 ) an d

a l ly l n ap h th a l en e (6 5 5 cm-1 ) , CH =CH 2 w ag o ccu rs i n th e reg io n 5 5 1 -5 5 8 c m -1 . Ac ry lo n i tr i le

an d d i v in y lsu l fon e exh i b i t C H= CH 2 w ag a t 6 8 0 an d 7 1 5

c m - 1 ,

respect ively , and oc cur a t h ighe r

f req u en cy t h an for co m p o u n d s o f fo rm (R - )3 C CH =C H2 . On t h e o t h e r h an d , a l l y lb en zen e an d

a l l y ln ap h t h a l en e exh ib i t CH=CH2 wag a t 6 4 8 an d 6 5 5 c m - 1 , respect ive ly , and occur a t h igher

frequency than for 1 -a lkenes of form

R - C H 2 - C H - C H 2

( 5 7 2 - 6 2 7

c m - 1 ) .

The reason for the

CH=CH2 wag f req u en cy b eh av io r wi th ch emica l s t ru c tu re i s a s fo l l o ws : Th e CH--CH2 wag

in c lu d es b en d in g o f t h e C - C - C b o n d s , an d a s t h e C ( - )2 b eco mes i n crea s i n g ly b ran ch ed i t

b eco mes mo re d i ff icu lt fo r t h e C- C - C g ro u p t o b en d o u t -o f -p lan e t o g e t h e r wi t h t h e th ree

hydr ogen a tom s jo ined to v iny l g roup bendin g out -of-p lane in the same d i rec t ion as the 3-carbon

atom. Therefore , CH=CH2 wag increases in f requency as the 3-carbon a tom is increas ing ly

branched . Apparen t ly , in the case of acry loni t r i le and d iv iny lsu l fone , i t i s more d i ff icu l t fo r the

C = C - C N a n d C = C - S b o n ds to b e n d t ha n f or ( R - ) 3 C - C = C b o n d b e n d in g i n t he c o m p le x

CH--CH2 wag v i b ra t io n .

B A N D A B S O R B A N C E R A T I O S A N D

F RE Q UE NC Y

S E P A R A T I O N S F O R V I N Y L T W I S T , V I N Y L C = C H 2 , A N D

V I N Y L C H = C H 2 W A G

Table 4 .2a and Table 4 .1 l i s t the numbers and frequencies for the normal v ibra t ions l i s ted in th i s

sec t io n (3 ) . Fo r 1 -a lk enes t h e ra t io o f t h e ab sorb an ces (A) fo r (A) CH =C H2 twi s t / (A )C= CH 2

wag i s i n t h e ran g e 0 .3 4 1 -0 .6 1 7 . Th i s sh o ws t h a t t h e C- -CH 2 wag mo d e h as mo re i n t en s i t y t h an

the CH=CH2 twis t mode. Table 4 .2a shows the same t rend except for acry loni t r i le and a l ly l

a lcohol where these two modes have essen t ia l ly iden t ica l in tensi ty .

In Tab l e 4 .1 i t i s n o t ed t h a t t h e f req u en cy sep a ra t i o n b e tween CH=CH2 twi s t an d C=CH2

wag v a r ie s b e t ween 8 0 an d 9 4

c m - 1 ,

and in Table 4 .2a i t var ies be tween 41 an d 80 cm -1 w i th the

except ion of 19 and 9

c m - 1

for acetonitri le and divinylsulfone, respectively.

Th e f req u en cy sep a ra t i o n b e tween CH=CH2 twi s t an d CH=CH2 wag v a r i e s b e tween 3 1 9 an d


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5 8 Alkenes and Other Compounds Containing C--C Double Bonds

I n t h e c as e of t h e f r e q u e n cy s e p a r a t i o n b e t w e e n C = C H 2 w a g a n d C H = C H 2 w a g i t v a ri e s

b e t w e e n 2 2 6 a n d 3 3 9 c m - 1 fo r 1 -a lkenes ( see Table 4 .1 ) . The f requency separa t ion fo r the 1 -

a lk en es n o t su b s t i t u t ed in t h e 3 - p o s i t i o n v a r i e s b e tween 2 8 6 an d 2 3 9 c m - 1 , wh i l e f o r t h o se

su b s t i t u t ed in t h e 3 - p o s i t i o n i t v a r i e s b e twe en 2 2 6 an d 2 5 7 c m - 1 ( see Table 4 .2a) .

R A M A N D A T A F O R X - C H = C H 2 C O M P O U N D S

T a b le 4 . 2 b co n t a i n s R a m a n d a t a a n d a s si g n m e n t s f o r X - C H = C H 2 c o m p o u n d s a n d f o r c is - a n d

t r an s - c r o to n o n i t r i l e . T h e n u m b er s i n p a r en th ese s a r e f o r t h e r e l a t i v e Ram an b an d in t en s i t i e s .

T h e y v a r y b e t w e e n 0 a n d 9 , n i n e b e i n g t h e m o s t i n t e n s e b a n d i n t h e s p e c t r u m , a n d 0 b e i n g t h e

l ea s t i n t en se b an d in t h e sp ec t r u m . As th e se a r e wh o le n u m b er s , i t d o es n o t d i f f e r en t i a t e b e tween

th e v a r i an ces i n i n t en s i ty f o r b an d s wh o se in t en s i t i e s l i e b e tween an y o f t h e wh o le n u m b er s ( 4 ) .

I n th e ca se o f c i s- an d t r an s - c r o to n o n i t r i l e t h e v C = C m o d es o c cu r a t 1 6 3 9 an d 1 6 2 9 c m - 1 ,

r e sp ec t iv e ly , an d th e Ram an b an d i s s t r o n g e r i n t h e ca se o f t h e t r an s i so m er th an f o r t h e c i s

i so m e r ( th e t r an s t o ci s r a t io i s 5 :4 ) . T h u s , t h e p o la r i za t io n o f t h e e l ec t r o n c lo u d d u r in g th e

vC--C v ibra t ion i s la rger fo r the t rans i somer than i t i s fo r the c is i somer .

C o m p a r i s o n o f t h e R a m a n d a t a f o r 1 - o c t e n e a n d 1 - d e c e n e s h o w s t h a t v C = C o c c u r s a t

1642 c m - 1 ; h o wev e r , i t is n o t ed th a t t h e b an d in t en s i ty i s 8 f or 1 - o c t en e an d 5 fo r 1 - d ecen e . T h e

em p i r i ca l s t r u c tu r e f o r 1 - o c t en e i s CH3- CH2)5-CH=CH2 and for 1 -decene is

CH3- CH2)F-CH=CH2. T h e CH2 g r o u p s a r e i n a 5 :7 in t h i s c a se wh i l e t h e b an d in t en s i ty

i s i n an 8 :5 f o r v C = C . T h i s i s wh a t i s ex p ec ted , b ecau se th e m o r e CH2 g r o u p s p r e se n t i n

1 - a lk en es th e s t r o n g e r t h e r e l a t i v e in t en s i ty f o r v C= C. Pe r h ap s th e r a t i o s wo u ld b e ex ac t ly 5 :7

an d 7 :5 i f t h e ex ac t b an d in t en s i t i e s we r e m eas u r ed .

C O N J U G A T E D V I N Y L G R O U P S

Vin y l - co n ta in in g co m p o u n d w h e r e th e v in y l g r o u p i s j o in e d d i r ec t ly to a c a r b o n a to m o f an

a r o m a t i c ri n g ex h ib i t s v C = C in th e r eg io n 1 6 2 9 - 1 6 3 3 - 1 ( T ab le 4 .2 b ) wh i l e 1 - a lk en es ex h ib i t

v C - - C a t h i g h e r f r e q u e n c y ( 1 6 4 1 - 1 6 5 3 c m - 1 ) . T h i s d e c r e a s e i n f r e q u e n c y i s a t t r i b u t e d t o

r e s o n a n c e o f t h e C = C g r o u p w i t h t h e a r o m a t i c ri n g. R e s o n a n c e w e a k e n s t h e s t re n g t h o f t he

C = C b o n d , w h i c h c a u s e s v C = C t o v i b r a t e a t l o w e r f r e q u e n c y .

T ab le 4 .2 b sh o w th a t t h e lo wes t v C- - C f r eq u en c ie s a r e f o r t h o se co m p o u n d s co n ta in in g th e

S i - C H = C H 2 g r o up ( v C = C , 1 5 9 0 - 1 6 0 3 c m - 1 ) . T h e R a m a n b an d i nt e ns i ti e s f or v C = C a re

r e l a t iv e ly in t h e weak - m ed iu m c l a ss . T h e v C= C f r eq u en cy f o r v in y l p h en y l su l f o n e i s a l so lo w

( 1 6 0 7 c m - 1 ) wh e r e th e v in y l g r o u p i s j o in ed to su l f u r ( 3 ) .


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Var iable s in Data Inte r pr e tat ion

5 9

R a m a n b a n d i n t h e r e g i o n 1 6 2 6 - 1 6 3 9 c m - 1 . I n th e I R, tw o ( o r s o m e t i m e s t h r e e) b a n d s a r e

o b s e r v e d i n th e v C = C s t r e t c h in g r e g i o n o f th e s p e c t r u m ( 5 ) . A n e x p l a n a t i o n i s r e q u i r e d t o

e x p l a i n th e e x i st e n c e o f t w o b a n d s i n th i s r e g i o n w h e n o n l y o n e O - C H = C H 2 g r o u p i s p r e s e n t i n

t he se mo l e c u l e s . The re a re t wo pos s i b i l i t i e s fo r t h i s obse rva t i on (p re sumi ng t he spe c t r a r e p re se n t

p u r e m a t e r i a ls ) , a n d t h e s e a re f o r th e p r e s e n c e o f r o t a t i o n a l c o n f o r m e r s o r f r o m b a n d s p l i tt i n g

d u e t o F e r m i r e s o n a n c e ( E R .) o f v C = C w i t h t h e f ir st o v e r t o n e o f a lo w e r l y i n g f u n d a m e n t a l o f

t h e C H = C H 2 g r o u p . C r i t e r i a f o r E R . t o o c c u r b e t w e e n a f u n d a m e n t a l a n d a c o m b i n a t i o n o r

o v e r t o n e o f a l o w e r l y in g f u n d a m e n t a l o r t w o l o w e r l y i n g f u n d a m e n t a l s a r e p r e s e n t e d i n w h a t

fo l lows (4) .

T h e c o m b i n a t i o n o r o v e r t o n e m u s t b e o f t h e s am e s y m m e t r y s p ec i es a s t h e v C = C v i b r a t i o n

a n d t h e c o m b i n a t i o n o r o v e r to n e m u s t i n v ol v e m o l e c u l a r m o t i o n w i t h i n t h e C H = C H 2 g r o u p . I n

a d d i t io n , v C = C a n d t h e c o m b i n a t i o n o r o v e r t o n e m u s t o c c u r a t s i m i l a r f r e q u e n c ie s i n o r d e r f o r a

s i g n if i ca n t a m o u n t o f E R . to o c c u r b e t w e e n v C = C a n d i t s c o m b i n a t i o n o r o v e r t o n e . I t d o e s n o t

m a t t e r i f t h e c o m b i n a t i o n o r o v e r t o n e o c c u r s a b o v e o r b e lo w t h e u n p e r t u r b e d v C = C v i b r a ti o n . I f

t h e c o m b i n a t i o n o r o v e r t o n e i s i d e n t i c a l i n f r e q u e n c y t o t h e u n p e r t u r b e d v C = C f r e q u e n c y , b o t h

R a m a n o r IR ba nd s wi l l ha ve e qua l i n t e ns it y . In o t he r wo rds , i n t h i s c a se bo t h b a nds r e su l t f rom

a n e q u al c o n t r i b u t i o n o f v C = C a n d a n e q u a l a m o u n t o f t h e c o m b i n a t i o n o r o v e r t o n e . B ec a u se

c o m b i n a t i o n o r o v e r t o n e s u s u a l l y h a v e i n t e n s it i e s a t le a st a n o r d e r o f m a g n i t u d e l es s t h a n m o s t

f u n d a m e n t a l v i b r a t io n s , a n e x p l a n a t i o n i s r e q u i r e d f o r th e o f t e n t w o s t r o n g b a n d s o r a s t r o n g a n d

m e d i u m b a n d i n t h e e v e n t o f E R . T h i s o c c u r s b e c a u s e t h e f u n d a m e n t a l c o n t r i b u t e s i n t e n s i t y t o

t h e c o m b i n a t i o n o r o v e r t o n e , w h i c h c a u s e s t h e p e r t u r b e d f u n d a m e n t a l t o b e w e a k e r t h a n i t s

u n p e r t u r b e d i n t e n s i t y a n d t h e p e r t u r b e d c o m b i n a t i o n o r p e r t u r b e d o v e r t o n e t o b e m o r e i n t e n s e

t ha n i t s unpe r t u rbe d i n t e ns i t y . I t i s u sua l p ra c t i c e t o a s s i gn t he mos t i n t e nse ba nd o f t he F e rmi

d o u b l e t a n d t h e w e a k e r b a n d t o th e c o m b i n a t i o n o r o v e r to n e . H o w e v e r , th e t r u t h o f t h e m a t t e r i s

t h a t b o t h b a n d s a r e in E R ., a n d b o t h m o d e s c o n t r i b u t e t o b o t h t h e b a n d f r e q u e n c i es a n d t h e

i n te n s it i es . T h e s t r o n g e r o f t h e b a n d s h a s m o r e c o n t r i b u t i o n f r o m t h e u n p e r t u r b e d f u n d a m e n t a l

a n d t h e w e a k e r o f th e b a n d s h a s t h e l e as t c o n t r i b u t i o n f r o m t h e f u n d a m e n t a l a n d t h e m o s t

c o n t r i b u t io n f r o m t h e u n p e r t u r b e d c o m b i n a t i o n o r o v e r t on e .

I t so ha ppe ns t ha t C =C H2 wa g fo r v i ny l phe n y l e t he r i s a s s igne d a t 850 c m -1 , a nd i ts f i rs t

o v e r t o n e w o u l d b e e x p e c t e d t o o c c u r a b o v e 1 7 0 0 c m - 1 . T h i s i s d u e t o t h e f ac t th a t C = C H 2 w a g

e x h i b i t s n e g a t i v e a n h a r m o n i c i t y ( o c c u r s a t h i g h e r f r e q u e n c y t h a n t w i c e t h e f u n d a m e n t a l

f r e q u e n c y ) ( 5 ). A v e r y w e a k b a n d i s n o t e d a t 1 7 1 0 c m - 1 i n t h e c as e o f v i n y l p h e n y l e t he r ,

a n d i t is r ea s o n a b l y a s s ig n e d a s 2 ( C = C H 2 w a g ) . T h e R a m a n b a n d a t 1 6 4 4 c m - 1 a n d t h e s t r o n g

1 6 4 3 I R b a n d a r e as s i g n e d t o a v C - C m o d e . A w e a k - m e d i u m I R b a n d i s n o t e d a t 1 6 1 5 c m - 1 .

Obv i ous l y , f rom bo t h t he i n t e ns i t i e s a nd f r e qu e nc i e s o f the se t w o IR ba nd s ne i t he r f i ts t he

c r i t er i a fo r ER . On t h i s ba s i s we a s s i gn t he 1643 c m -1 ba n d t o v C - -C fo r the ga u c he c on f o rm e r

a nd t he 1615 r -1 bond t o t he ci s c on fo rm e r fo r v i ny l phe ny l e t he r (5 ,6 ) . The re fo re , t he v i ny l

a l k y l e t h e r s ex h i b i t g a u c h e v C = C i n t h e r e g i o n 1 6 3 6 - 1 6 3 9 c m - 1 a n d c i s v C = C i n t h e r e g i o n

1 6 1 0 - 1 6 2 0 c m - 1 .


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60 Alkenes and Other Compounds Containing C--C D ouble Bonds

In the vapor-phase , vasym. CH2-- for v iny l a lky l e thers occur in the reg ion (3122-

3 1 3 5 c m - 1 ) , v C H = o c c u r s i n t h e r e g i o n ( 3 0 6 0 - 3 0 7 0 c m - 1 ) , v s y m . CH2= in the reg ion

( 2 9 8 4 - 3 0 1 5 c m - 1 ) ,

CH2=

b e n d i n t h e r e g i o n ( 1 4 0 0 - 1 4 1 8 c m - 1 ) , C H = r o c k i n t h e r e g i o n

( 1 3 1 1 - 1 3 2 1 c m - 1 ) , C H = C H 2 t w i s t i n t h e r e g i o n ( 9 6 1 - 9 6 5 c m - 1 ) , C = C H 2 w a g i n t h e r e g i o n

( 8 1 2 - 82 5 c m - 1 ) , c i s - C H = C H 2 w a g i n t he re g io n ( 6 87 - 7 0 1 c m - 1 ) , va sy m . C = C - O - C i n t he

r e gi on ( 1 2 0 3 - 1 2 2 0 c m - 1 ) , a n d v sy m . C = C - O - C i n t he r e gi o n ( 8 3 7 - 8 8 8 c m - 1 ) .

1 - A L K E N E ( C H - - C H 2 ) C H A N D C H 2 S T R E T C H I N G

V I B R A T I O N S

The carbon hydrogen s t re tch ing frequencies for 1 -a lkenes a l l t ake p lace wi th in the p lane of the

C=C g ro u p (Tab l e 4 .2 b ) .

Th e Ram an b an d i n t h e reg i o n 3 1 2 0 - 3 1 2 2 cm -1 w i t h t h e re l a ti v e i n t en s it y b e t ween 0 an d 2 is

a s s i g n ed t o v a sym. CH 2 --, t h e Ram an b an d i n t h e reg i o n 3 0 4 3 -3 0 4 6 cm -1 w i th t h e re l at iv e b o n d

in t en s i ty b e tween 1 an d 4 i s a s s i g n ed t o v CH= , t h e Raman b an d i n t h e reg io n 3 0 2 2 -3 0 2 3 cm -1

wi th a re la t ive in tensi ty be tw een 1 and 2 is ass igned to vsym. CH2=, an d t h e Raman b an d i n t h e

reg io n 1 3 2 0 -1 3 2 9 c m -1 wi t h a rel a ti v e in t en s i t y b e tween 2 an d 9 i s a s s i g n ed CH = in -p l an e

ro ck i ng . Th e CH = i n -p lan e ro c k in g m o d e fo r v i n y l p h en y l e t h e r i s a ss i g n ed a t 1 3 1 1 cm -1 .

C = C H 2 W A G F R E Q U E N C I E S V S ( S I G M A p - S I G M A ' )

The te rm (s igma p-s igma ' ) def ines the induct ive effec t o f G for G-CH=CH2. Table 4 .3 l i s t s the

C=CH 2 wag frequencies and the induct ive va lue of g roup G. The posi t ive va lues wi thdraw s igma

elec t rons from the v iny l g roup , the negat ive va lues cont r ibu te s igma e lec t rons to the v iny l g roup .

A p lo t o f the

C-'CH2

wag f req u en c i e s v s r rp - r r ' sh o ws a smo o th re l a t i o n sh ip (5 ) .

C H = C H 2 T W I S T F R E Q U E N C I E S V S o A N D p K a O F G F O R

G - C H 2 C O 2 H

Table 4 .3a l is t s IR CS2 so lu t ion and IR vapor-ph ase da ta for C H =C H 2 twis t f requencies , pK a of


7/37

Variables in Data Interpretat ion 61

A L L Y L H A L I D E S

Table 4 .4 l is t s the IR da ta an d ass ig nme nts for the c i s and gauche conform ers of the a l ly l ha l ides .

In al l c a se s , c is v C -C (1 6 4 5 -1 6 5 2 c m - 1 ) o c c u r s a t h i g h e r f r e qu e n c y th a n g a u c h e v C - C ( 1 6 3 0 -

1 6 4 3 cm -1 ) (7 ). Ho wev e r , t h e f req u en cy sep a ra ti o n fo r g au ch e C H= CH 2 twi s t an d g au ch e

C--CHz wag i s n ea r l y co n s t an t (4 8 .2 -4 8 .9 cm-1 ) . An i n t e re s t i n g co r re l a t i o n ex i s t s fo r t h e

f req u en cy sep a ra t i o n b e tween g au ch e CH=CH2 twi s t an d g au ch e CH=CH2 wag i n t h a t i t

i n c r e a s e s i n t h e o r d e r F ( 3 4 7 c m - 1 ) , C 1 ( 3 9 5 . 2 c m - 1 ) , B r ( 4 4 6 . 2 c m - 1 ) , a n d I ( 4 8 9 . 7 c m - 1 ) . T h e

f req u en cy sep a ra t i o n b e t ween g au ch e C=CH2 wag an d g au ch e CH=CH2 wag i n c rea se s i n t h e

same order : F(292 .7 c m - 1 ) , C1(347 cm -1) , Br(397 .3 cm -1) , and I(440 .8 c m - 1 ) . Th e g au ch e

CH=CH2 wag frequency i s the most a ffec ted progress ing in the order F th rough I fo r these

a l ly l ha l ides , because the f requency separa t ion be tween F and C1 i s 52 .3 c m - 1 , C1 and Br is

52.3 c m - 1 , and Br and I is 46 .5 cm -1 . In th i s case the induct ive effec t o f the ha logen a toms

d ec rea se s in t h e o rd e r F to I wh i l e t h e mass i nc rea se s i n t h e same o rd e r . Th e C - C = b o n d

st rength decreases in the order F to I due to the decreas ing induct ive effec t of the ha loge n a tom s,

wh ich cau ses CH--CH2 wag to o ccu r a t a l o wer f req u en cy b ecau se t he C - C = b o n d i s mo re

easi ly b en t d u r in g t h i s co mp l ex C H= CH 2 wag fu n d am en t a l .

C Y C L O A L K E N E S A N D C Y C L O A L K A D I E N E S

Table 4 .5 l i s t s IR da ta and C=C or (C=C)2 s t re tch ing ass ignments for cyc lopentene , cyc lohex-

ene , 1 ,4-cyclohexadiene , and 1 ,3-cyclohexadiene in mole % CHC13/CC14 so lu t ions (8) . Only

three da ta po in ts a re l i sted in the table , bu t 20 da ta po in ts were tak en in the or ig ina l expe riment .

F ig u re 4.1 sh o ws t h e p lo t o f th e v C =C o r v (C= C)2 mo d es v s mo le % CDC1 3 /or CH C1 3 / so lven t

system.

Th e v C =C mo d e fo r cy c lo p en t en e (1 6 1 3 .9 t o 1 6 1 1 .2 cm -1 ) an d cy c l o h exen e (1 6 5 2 .8 t o

1650.9) decreases in f requ ency as the m ole % CHC 13 increases . These da ta suggest tha t the

s t ren g th o f t h e i n t e rmo lecu l a r p ro to n b o n d fo rmed b e tween t h e C=C g sy s t em an d t h e H o r D

atom of CHC13 or CDC13 increases as the mole % CH C13 or CDC13 increases . In addi t ion the

s lopes of the p lo ts for cyc lopentene and cyclohex ene are essen t ia lly iden t ica l . T he re la t ive ly la rge

frequency d i fference be tween tha t fo r cyc lopentene and cyclohexene does no t represen t the

b as i c i t y o f t h e C=C b o n d . Th e ma jo r fac to r i n d e t e rmin in g t h e v C=C f req u en cy i s t h e b o n d

an g le s o f t h e ca rb o n a to ms j o i n ed t o c is C= C (9 ). Th e v C =C f req u en cy ch an g es ran d o mly i n t h e

o r d e r c y c lo p r o p e ne ( 1 6 5 6 c m - 1 ) , c y c lo b u te n e ( 1 5 6 6 c m - 1 ) , c y c lo p e n te n e ( 1 6 1 3 . 9 c m - 1 ) , a n d

cy c l o h exen e (1 6 5 2 .8 cm -1 ) (9 ,1 0 ) .

Bo th 1 ,4 - an d 1 ,3 -cy c lo h exad i en es co n t a in t wo C =C d o u b l e b o n d s , an d i n each ca se t h e C= C

b o n d s co u p l e an d sp l i t i n t o o u t -o f -p h ase (C=C)2 s t re t ch in g an d i n -p h ase s t re t ch in g (8 ) .


8/37

6 2 Alkenes and Other Compounds Containing C--C Double Bonds

Vip Occ urs a t 1676 .8 cm -1 a nd Vop(C=C) 2 occu rs a t 1637 .9 cm -1 . In th is case , i t i s t h e Yip(C-~C)2

f r eq u en cy th a t i n c r ea se s 4 .5 cm - 1 w h i l e t h e Vo p ( C= C) f r eq u e n cy d ec r ea se s 1 .3

c m - 1 .

Ho wev e r ,

F ig u r e 4 .1 sh o ws th a t t h e h ig h e r f r eq u en cy b an d in each se t i n c r ea se s i n f r eq u en cy wh i l e t h e

lo wer f r eq u en cy b an d in each se t d ec r ea se s i n f r eq u en cy g o in g f r o m th e n ea t p h ase to d ec r ea s in g

co n c en t r a t io n in C HC1 3 o r CDC1 3 so lu t io n s ( 8 ).

I n t h e ca se o f 1 ,3 - cy c lo h ex ad ien e , t h e two C= C g r o u p s a r e co n ju g a ted

C H - - C H - C H = C H 2

wh i l e i n t h e ca se o f 1 ,4 - cy c lo h ex ad ien e th e two C= C g r o u p s a r e n o t co n ju g a ted . Fo r t h e sak e o f

c o m p a r i s o n , t h e r ip C--C) 2 an d Vo p ( C= C) 2 m o d es f o r s - t r an s - b u tad ien e in t h e l i q u id p h as e

o ccu r a t 1 6 3 8 an d 1 5 9 2 cm - 1 , r e sp ec t iv e ly ( 1 0 ). T h e c o m p o u n d , c i s 2 - t e r t - b u ty lb u tad ien e ,

ex h ib i t s

r ip C--C) 2

a n d

Vop C=C) 2

a t 1 6 1 0 an d 1 6 4 5 cm - 1 , r e sp ec t iv e ly . T h e r e f o r e , t h e

v ip ( C= C) 2 an d Vo p ( C= C) 2 f r eq u en cy o r d e r i s t h e sa m e f o r 1 ,3 - cy c lo h ex ad ien e an d c i s t e r t -

bu ty lbu tad iene . In th is case , the two C-- -C groups have to be in a c is-c is conf igura t ion due to r ing

r e s t r a in t , an d th i s i s i n g o o d ag r eem en t w i th th e c i s co n f ig u r a t io n a ss ig n m en t f o r c i s - t e r t -

b u t y l b u t a d i e n e .

T ab le 4 .5 a l i s t s I R v ap o r - p h ase d a t a f o r c i s - cy c lo a lk en e d e r iv a t iv e s . Cy c lo p en ten e ex h ib i t s

v C = C a t 1 6 2 1

c m - 1

i n t h e v a p o r p h a s e a n d 1 6 1 4 c m - 1 i n

C C I 4

s o l u t i o n , a n d c y c l o h e x e n e

ex h ib i t s v C= C a t 1 6 5 1 c m - 1 i n t h e v ap o r p h ase an d 1 6 5 3 c m - 1 in CC14 so lu t ion . In th is case the

v C- - C m o d e f o r t h e so lu t io n - p h ase d a t a r ead d i r ec t ly f r o m th e co m p u te r a r e co n s id e r ed m o r e

accu r a t e t h a n th e m an u a l ly r ead v ap o r - p h ase d a t a . I f t h e se d a t a a r e v a l id , t h e co r r e l a t io n o f

v C= C o ccu r r in g a t h ig h e r f r eq u en cy in t h e v ap o r t h an in so lu t io n i s an ex cep t io n in t h e ca se o f

cy c lo h ex en e .

A s tu d y o f T ab le 4 .5 a sh o ws th a t v C- - C f o r t h e 5 - m em b er ed r in g s o ccu r a t t h e l o wer

f r eq u en cy th an th o se f o r t h e 6 - m em b er ed r in g s a s a l r ead y d i scu ssed h e r e . Co m p ar i so n o f t h e

v C = C v i b r a ti o n s f o r 2 - c y c l o p e n t e n e - l - o n e a n d 2 - c y c l o h e x e n e - l - o n e ( 1 6 0 0 c m - 1 v s 1 6 24 c m - 1 )

sh o ws th a t v C= C f o r t h e 5 - m em b er ed r in g s t i l l o ccu r s a t l o wer f r eq u en cy th an i t d o es f o r t h e 6 -

m e m b e r e d r i n g . H o w e v e r , b o t h v C - - C m o d e s a r e l o w e r i n f r e q u e n c y t h a n f o r c y c l o p e n t e n e

( lo wer b y 2 1 c m - 1 ) an d f o r cy c lo h ex en e ( lo wer b y 2 7 c m - 1 ) . T h e r ea so n f o r t h i s i s t h a t t h e C= C

a n d C = O b o n d s a r e c on j u g a t ed , w h i c h c a u s e s b o t h b o n d s t o b e c o m e w e a k e r a n d t h e c o n n e c t i n g

C - C b o n d to b eco m e s t ro n g e r . T h e r e f o re , v C = O a l so o ccu r s a t l o wer f r eq u en cy in th e ca se o f 2 -

cy c l o p e n ten e - l - o n e ( 1 7 4 5 cm - 1 ) v s ( 1 7 6 5 cm - 1 ) f o r cy c lo p en tan o n e in t h e v ap o r p h ase an d 2 -

c y c l o h e x e n e - l - o n e ( 1 7 1 0 c m - 1 ) v s ( 1 7 3 2 c m - 1 ) f o r c y c l o h e x a n o n e i n t h e v a p o r p h a se . I n t h e

v C= O case s , t h ey a r e l o wer b y 2 0 an d 2 2 c m - 1 f o r t h e 5 - an d 6 - m em b er ed r in g s , r e sp ec t iv e ly .

T h e r e f o r e , c o n j u g a t i o n o f C - - C w i t h C = O d e c r e a s e s b o t h m o d e s i n t h e s a m e o r d e r o f

m a g n i t u d e .

A n I R b a n d i n t h e r e g io n 6 9 9 - 7 5 0 c m - 1 i s as s i g ne d t o c i s C H = C H w a g i n t h e s i x c is

c o m p o u n d s s t u d ie d . A n o t h e r b a n d i s n o t e d i n t h e r e g i o n 6 3 5 - 6 5 8 c m - 1 . I t i s n o t c e r t a i n w h e t h e r

th e se b an d s r e su l t f r o m a d i f f e r en t v ib r a t io n a l m o d e o r f r o m c i s CH- - CH wag o f an o th e r

co n f o r m er .


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Variables in Data Interpretation

63

s o lu t ion , c i s vC=C i s a s s igned in the r eg ion 1619 . 2 -1620 . 4 c m - 1 , and in CHC13 s o lu t ion , in the

r e g i on 1 6 1 8 . 5 - 1 6 1 9 . 9 c m - 1 I n

C C 14

s o lu t ion , t r ans vC=C occur s in the r eg ion 1635 . 3 -

163 7 . 2cm -1 , and in C HC13 s o lu t ion in the r eg ion 163 5 . 1 - 163 6 . 6c m -1 . In a ll cases c is vC =C

o c c u r s a t l o w e r f r e q u e n c y t h a n t r a n s v C = C , a n d b o t h c i s a n d t r a n s v C = C o c c u r a t l o w e r

f r equency in CHC13 than in C C 14 s o lu t ion .

Tab le 4 . 6a l i st s IR da ta and as s ignm en ts fo r a lky l me thacry la tes in

C C I 4

and CHC13 s o lu t ion

(11) . In CC 14 s o lu t ion v C= C fo r the a lky l me tha cry la tes occ ur s in the r eg ion 1635 . 7 -

1 6 3 7 . 3 c m - 1 , i n C H C 1 3 s o l u ti o n , v C = C o c c u r s i n t h e r e g i o n 1 6 3 5 . 7 - 1 6 3 7 . 3 c m - 1 , a n d i n

CHC13 s o lu t ion , v C= C occur s in the r eg ion 1635 . 8 -1 637 . 3 cm -1 . In a l l cas es vC- -C occur s a t

lower f r equenc y in CHC13 than in C C 14 s o lu t ion by 0 . 8 to 2 . 3 c m - 1 .

The vC=O f r equenc ies fo r the a lky l me thacry la tes occur in the r eg ion 1719 . 5 -1726

c m - 1

( in

CC14) and 17 09 . 5 -17 18 cm -1 ( in CHC13). Thus , vC - -O occur s a t lower f r equency by 8 to

1 0 . 6 c m - 1 i n g o i n g f r o m C C 14 to CHC13 s o lu t ion . T he vC- -O f r equenc ies fo r a lky l ac ry la tes

occur in the r eg ion 1722 . 9 -1734 . 1 c m - l l ( i n C C 14 ) and in the r eg ion 1713 . 8 -1724 . 5 c m - 1 ( in

C H C 13 ). T h u s , t h e v C = O o c c u r s a t l o w e r f r e q u e n c y b y 3 . 4 - 1 0 . 8 c m - 1 i n g o i n g f r o m C C 1 4 t o

CHC13 s o lu t ion (11 ) . In the vapor phas e v C= O fo r me thy l me tha cry la te and m ethy l ac ry la te

occur a t 1741 and 1751

c m - 1 ,

r es pec t ive ly (2 ) . Thes e da ta s how tha t the vC=O f r equenc ies

occur a t h igher f r equency in the vapor phas e than in s o lu t ion .

I t s h o u l d b e n o t e d f r o m t h e p r e c e d i n g v C - O f o r t h e m e t h a c r y l at e s o c c u r a t l o w e r f re q u e n c y

than fo r the ac ry lates. Th i s s h i f t to lower f r eque ncy i s a t t r ibu ted to the induc t ive co n t r ibu t io n o f

t h e C H 3 g r o u p t o t h e c a r b o n y l g r o u p , w h i c h w e a k e n s t h e C = O b o n d .

I t s hou ld be a l s o no ted tha t the a lky l g roup a l s o caus es a s h i f t in the vC=O f r equency . F o r

example, in the case of a lkyl acrylates in C C I 4 s o lu t ion , vC=O occur s a t 1734 . 1 , 1727 . 3 , 1727 . 1 ,

and 1722 . 9

c m - 1

for the methyl , butyl , 2-ethylhexyl , and ter t -butyl analogs , respect ively . In the

case of the same ser ies of a lkyl methacrylates in

C C I 4

s o lu t ion , vC=O occur s a t 1718 , 1710 . 5 ,

and 1709.5 , respect ively . These vC--O f requency decreases a lso are a t t r ibuted to the increased

induc t ive con t r ibu t ion o f the a lky l g roup p rogres s ing in the s e r i e s methy l to t e r t -bu ty l .

In the case o f a lky l ac ry la tes , the C H2= bend occur s in the r eg ion 1401 . 6 -1407 . 2 c m - 1 ( in

CC14) and in the r eg ion 1404-1 410 . 3 cm -1 ( in CHC13). Thus CH 2= ben d inc reas es in f r equency

by 2 . 4 to 3 . 4 cm -1 on go ing f rom CC14 to CHC13 s o lu t ion .

A lky l ac ry la tes exh ib i t C H2 =C H tw is t in the r eg ion 9 82 . 6 -9 84 . 9 cm -1 ( in CC14) and 983 . 4 -

985 cm -1 ( in CHC13) . The C= CH 2 wag f r equenc ies occur in the r eg ion 9 66 . 3 -9 68 . 4 cm -1 ( in

CC14) an d 966 .5-9 70 .3 cm -1 ( in CHC13) .

T R A N S - A L K E N E S

Tab le 4 .7 l i st s IR vapor -phas e f r equency da ta fo r tr ans -a lkenes an d c om pou nds con ta in ing a


10/37

64 A l k e n e s a n d O t h e r Compounds Containing C - - C D o u b l e Bonds

W h e n t h e R g r o u p s o r X g r o u p s a r e i d e n t i c a l t h e v C = C i s n o t a l l o w e d i n t h e I R , b e c a u s e t h e s e

c o m p o u n d s h a v e a c e n t e r o f s y m m e t r y . T h e r e fo r e , t h e r e i s n o d i p o l e m o m e n t c h a n g e d u r i n g a

c yc le o f vC - -C . How e ve r , i n th i s c a se t he vC =C m ode i s R a m a n a c t ive . Howe v e r , e ve n i n the c a se

w h e r e t h e t r a n s - a l k e n e s d o n o t h a v e a c e n te r o f s y m m e t r y , th e d i p o l e m o m e n t c h a n g e d u r i n g a

c yc l e o f t r a ns v C =C i s sma l l , a nd t he IR ba n d i s ve ry we a k . R a m a n spe c t ro sc o py i s r e qu i re d t o

re a d i l y de t e c t t he C - -C i n t r a ns -a l ke ne s .

o R

\ \ /

H3C

A l k y l c r o t o n a t e s e x i s t i n a t r a n s c o n f i g u r a t i o n , a n d i n t h e v a p o r p h a s e t r a n s v C = C o c c u r s n e a r

1 6 6 4 c m - 1 . A w e a k b a n d a t 1 6 4 9 c m - 1 a n d a w e a k - m e d i u m b a n d i s n o t e d a t 1 6 2 1 c m - 1 i n t h e

v a p o r - p h a s e s p e c t r u m o f c i n n a m o n i t r i l e , s u g g e s t i n g t h a t b o t h t h e c is a n d t r a n s i s o m e r s a r e

p re se n t .

T h e t r a n s C H = C H t w i s t i s a s s ig n e d i n t h e r e g i o n 9 6 1 - 9 7 2 c m - 1 f o r m o s t o f t h e se c o m p o u n d s

i n c l u d e d i n Ta b le 4 .7 . H a l o g e n a t o m s jo i n e d t o C = C l o w e r s t he t r a n s C H = C H t w i s t m o d e . F o r

e x a m p l e , i t o cc u r s a t 8 9 7 c m - 1 f o r t r a n s - l , 2 - d i c h l o r o e t h y l e n e a n d a t 9 3 0 c m - 1 f o r 1 , 3 -

d i c h l o rop rope ne ; Ta b l e 4 .8 l i s t s da t a fo r a va r i e t y o f t r a ns d i subs t i t u t e d e t hy l e ne s i n C S 2

s o l u t i o n i n m o s t c a s es ( 5 ) . T h e t r a n s C H = C H t w i s t m o d e o c c u r s i n t h e r e g i o n 8 9 6 - 9 7 5 c m - 1 .

A L K Y L C I N N A M A T E S

Ta b l e 4 .9 li s ts IR va po r -pha se d a t a fo r a l ky l c i nna m a t e s (3 ) . The v C =C v i b ra t i on o c c u r s i n t he

r e g i o n 1 6 4 0 - 1 6 4 2 c m - 1 i n t h e v a p o r - p h a s e , a n d i t h a s m e d i u m b a n d i n te n s it y . T h e C H - - C H

t w i s t o c c u r s i n t h e r e g i o n 9 7 2 - 9 8 2

c m -1 ,

a nd i t s i n t e ns i t y i s a l wa ys l e s s t ha n t ha t e xh i b i t e d by

v C = C a s d e m o n s t r a t e d b y t h e a b s o r b a n ce r at io [ ( A ) H C - C H t w i s t ] / [ ( A ) v C = C ] i n t h e r a n g e

0 . 4 2 - 0 . 6 7 . T h e v C - - O m o d e f o r t h e s e al k y l c i n n a m a t e s w i l l b e d i s c u s s ed i n C h a p t e r 1 5.

C I N N A M Y L E S T E R S

Ta b l e 4 .10 l i st s IR va po r -pha se da t a fo r c i nna my l e s t er s (3 ) . In t h i s c a se , vC =C oc c u r s i n t he

r e g i o n 1 6 5 2 - 1 6 6 0 c m - 1 , a n d i t o c cu r s a t h i g h e r f r e q u e n c y t h a n i n t h e c a s e o f a l k yl c i n n a m a t e s

( c o m p a r e w i t h d at a i n T a bl e 4 . 10 ) . I n th e ca se o f a lk y l c i n n a m a te , ~ - C H - - C H - C ( = O ) - O - R ,

t h e C - - O a n d C - - C g r o u p s a r e c o n j u g a t e d c a u s i n g b o t h v C - - C a n d v C = O t o o c c u r a t l o w e r


11/37

Var iable s in Data Inte r pr e tat ion 6 5

1 , 1 - D I S U B S T I T U T E D E T H Y L E N E S

Table 4.11 lis ts IR data for

C = C H 2

wag an d i t s fi rs t over tone fo r 1 , 1 -d i s ubs t i tu ted e thy lenes (5 ) .

The fun dam en ta l i s r eco rded in CS 2 s o lu t ion an d i t s over tone in CCI4 s o lu t ion . The C- -CH2 wag

m o d e o c c u r s i n t h e r e g i o n 7 1 1 - 1 0 0 4 c m - 1 , a n d i t s fi rs t o v e r t o n e o c c u r s i n t h e r e g i o n 1 4 0 0 -

2 0 2 0 c m - 1 . T h e C = C H 2 w a g f r e q u e n c y e x h i b i ts n e g a ti v e a n h a r m o n i c i t y b e c a u s e t h e f ir st

over tone occur s a t more than tw ice the C- -CH2 wag f r equency .

In f r a red and Raman s pec t r a fo r 1 -b romo- l - ch lo roe thy lene a r e s hown in F igu re 4 . 2 , and thes e

da ta were us ed to as s ign i ts 12 fundame n ta l v ib ra t ions (13 ) . Com par i s o n o f thes e da ta w i th thos e

fo r 1 , 1 -d ich lo roe thy lene (14 , 15 ) and 1 , 1 -d ib romoethy lene (16 ) s how tha t 9 fundamen ta l s

decreas e in the o rd e r C12 , C1Br , and Br2 , and th i s t r end i s o f t en obs e rved in o the r ha logena ted

analogs (see Table 4 .11a) .

Tab le 4 . 12 l i s ts Ram an da ta a nd as s ignm en ts fo r the v iny l e s te rs o f ca rboxy l ic ac ids in the ne a t

p h a s e ( 4 ) . W i t h t h e e x c e p t i o n o f v i n y l c i n n a m a t e ( v C - C a t 1 6 3 6 c m - 1 ) a l l o f t h e o t h e r v i n y l

e s te r s e x h ib i t v C = C i n t h e r eg i o n 1 6 4 4 - 1 6 4 8

cm -1.

In a ll cases where the a l ipha t i c g rou p o f the

es te r i s s a tu ra ted the vC-C mode has much h igher r e la t ive in tens i ty (RI ) than the (RI ) fo r

vC- -O . The r a t io [ RI)vC--O]/[ RI)vC--C] i s in the r ange 0 . 11 -0 . 29 . In cas es where the

ca rboxy la te po r t ion o f the es te r i s con juga ted w i th the C=C g roup th i s RI r a t io va r ies f rom

0.22 to 2.

T h e f r e q u e n c y s e p a r at i o n b e t w e e n v C - C a n d v C - O v a r ie s b e t w e e n 9 8 a n d 1 1 0 c m - 1 f o r

c o m p o u n d s o f f o rm R - C ( - - O ) - O - C H - - C H 2 , a n d b e tw e e n 8 4 a n d 9 2 c m -1 i n c as es w h e r e t h e

C = O i s c o n j u g a t e d w i t h C - C o r a n u n s a t u r a t e d r i n g . T h i s d i f f e r e n c e i n t h e l o w e r f r e q u e n c y

s e p ar a ti o n is a t tr i bu t e d to r e so n a n ce b e tw e e n t he C - C a n d C = O g r o u p s ( C - C - C - O ) .

S T Y R E N E S A N D ~ - M E T H Y L S T Y R E N E S

Tab le 4 . 13 l i s t s Raman da ta and as s ignmen ts fo r s ty rene , s -methy l s ty rene monomers in the

con dem ned phas e (4 ). The vC- -C v ib ra t ion occur s in the r eg ion 1 62 4-1 63 5c m -1 . The 0~-

m e t h y l s ty r e n e ( v C - C , 1 6 3 1 c m -1) and 1 ,3-di(0~-methyl) s tyren e (1631 cm -1) exh ibi t vC --C

f requenc ies comparab le to s ty rene . However , vC =C o f thes e com pou nds occur lower in

f r e q u e n cy t h a n f o r 1 - oc t e ne ( 1 6 4 2 c m - 1 ) , a n d t h i s i s t h e re s u l t o f c o n j u g a t i o n b e t w e e n v C - C

and the pheny l g roup . O ther Raman bands l i s t ed in th i s t ab le a r e as s igned to in -p lane pheny l

r ing v ib ra t ions .

Tab le 4 . 14 l i s t s IR g roup f r equency da ta and as s ignmen ts fo r s ty rene and r ing - s ubs t i tu ted

s ty renes (12 ) . On ly da ta fo r s ty renes tha t had co r r e s pond ing r ing - s ub s t i tu ted ph eno ls w hos e pK a

va lues were inc luded were t aken f rom Refe rence 12 . F igu re 4 . 3 g ives the C- -CH2 wag

f requenc ies p lo t t ed aga ins t the pK a va lue o f the co r r es p ond ing r ing - s ubs t i tu ted pheno l .


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6 6 A l k e n e s a n d O t h er C o m p o u n d s C o n t a in i n g C - C D o u b l e B o n d s

induc t ive e f fec ts o f the a tom s or g roup s sub st i tu te d in the 2 ,6 -po si t ions tha t a re a f fec t ing the

C = C H 2

wag f r eq u en c ie s ( a s su m in g th a t t h e e f f ect s o f i n t r am o lecu la r f o rce s b e tween a to m s o r

g r o u p s in t h e 2 ,6 - p o s i t i o n s an d th e v in y l g r o u p a r e n eg l ig ib l e ) . T h e

C = C H 2

wag f r eq u en c ie s a r e

a f f ec t ed b y b o th in d u c t iv e an d r e so n an ce e f f ec t s i n ca se s wh e r e s ty r en es a r e n o t su b s t i t u t ed in

the 2 ,6 -posi t ions .

F ig u r e 4 .4 i s a p lo t o f t h e f r eq u en cy sep a r a t io n b e tween CH= CH2 twi s t an d C - - C H 2 wag for

s ty r en e an d r in g - su b s t i t u t ed s ty r en es v s t h e sam e p K a v a lu e s. A g a in , sep a r a t e co r r e l a t io n s ex i s t

f o r t h e p l an a r an d n o n p lan a r s ty r en es w i th th e ex cep t io n o f 2 ,4 ,6 - t r im e th y l s ty r en e , wh e r e th e

f r eq u en cy sep a r a t io n b e tween CH= CH2 twi s t an d C= CH2 wag i s l e s s t h an f o r t h e co r r e sp o n d in g

2 ,6 - d i su b s t i t u t ed p h en o l s wh o se p K a v a lu e s a r e l o wer t h an ~ , 7 .2 .

Table 4 .15 l i s t s IR da ta fo r 0~-halosty renes , 0~-a lky ls ty renes , and re la ted compounds (12) .

F ig u r e 4 .5 sh o ws a p lo t o f th e CH2 wag f r eq u en c ie s f o r s ty r en e an d r in g - su b s t i t u t ed s ty r en es v s

the

C--CH2

wag f requency for 0~-methy ls ty rene and cor responding ly r ing-subst i tu ted 0~-methy l-

s ty renes . Th is p lo t suggests tha t the fac to rs a f fec t ing

C--CH2

wag f o r b o th s ty r en es an d a - m e th y l

s ty r en es a r e co m p ar ab le . Ho wev e r , t h e CH2 wag f requencies fo r 0~-methyl s ty ren e oc cur a t low er

f r eq u en cy th an th e co r r e sp o n d in g ly su b s t i t u t ed s ty r en es b y 1 0 - 1 8 cm - 1 . T h e 0 ~- m e th y ls tyr enes

are no t p la nar fo r those subst i tu ted wi th C1 or CH3 in the 2 -posi t ion , w hi le fo r s ty rene s i t takes

su b s t i t u t io n in t h e 2 ,6 - p o s i t i o n s in o r d e r t o s t e r i c a l ly p r ev en t t h e v in y l an d p h en y l g r o u p s f r o m

being cop lanar .

B U T A D I E N E S , P R O P A D I E N E S , C O N J U G A T E D C Y C L I C

D I E N E S

T ab le 4 .1 6 l i st s IR v ap o r - p h ase d a t a an d a ss ig n m en t s f o r b u tad ien es an d p r o p ad ien es ( 3 ,1 7) .

C o m p o u n d s c o n t a i n in g t he 1 , 3 -b u t a di e n e s t r u c t u re a re o f f o r m C = C - C = C , a n d th e t w o C = C

b o n d s co u p le d u r in g th e i r

v ( C = C ) 2

v ib r a t io n s in to in - p h ase r ( C= C) 2 an d o u t - o f - p h ase

v(C=C)2 . I n t h e ca se s o f 1 ,3 - b u tad ien e an d 2 - m e th y l - l , 3 - b u tad ien e ip v ( C = C ) 2 o c c u r a t 1684

an d 1 6 4 9 cm - 1 , r e spec t iv e ly, wh i l e o p v ( C = C ) 2 o ccu r a t 1 5 9 4 an d 1 6 0 2 cm - 1 , r e sp ec t iv e ly.

Oth e r v ib r a t io n a l a s s ig n m en t s a r e p r e sen ted f o r t h e se two m o lecu le s .

P r o p a d i e n e s h a v e t h e b a s i c s k e l e t a l s t r u c t u r e C = C = C , a n d e x h i b i t i p ( C = C ) 2 a n d o p

v(C- -C)2

vibra t ional m ode. In the case o f p ropa d iene , the ip

v ( C = C ) 2

i s no t IR ac t ive due to

i ts m o lecu la r sy m m et r y . W i th su b s t i t u t io n o f an a to m o r g r o u p in t h e 1 - p o s i ti o n o f p r o p ad ien e ,

th e se m o lecu le s h av e o n ly a p l an e o f sy m m et r y , an d ip v ( C= C) o ccu r s i n t h e i r r eg io n 1 0 7 2 -

1 1 01 cm - 1 p r o g r e ss in g in f r eq u en cy in t h e o r d e r

CH 3, I ,

Br , an d C1 . T h e o p v ( C= C) m o d e i s

a l lo wed in I R f o r p r o p ad ien e , an d i t s m o n o su b s t i t u t ed d e r iv at iv e s , an d i t o ccu r s i n t h e r eg io n

1 9 5 3 - 1 6 6 3 cm - 1 ( 1 8 ) .

T h e co m p o u n d 2 ,5 - n o r b o r n ad ien e h a s t h e f o l lo win g b as i c s t r u c tu r e :


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V ar i ab l e s i n D a ta In t e rp re t a t i on 67

1 , 3 -cyc lohexad iene the r ing i s l a rge r than in the cas e o f the 2 , 5 -norbornad ienes . The 6 -

membered r ing i s no t fu s ed in th i s cas e , bu t the two C=C g roups a r e con juga ted . The ip

v (C=C)2 and op modes a r e as s igned a t 1600 and 1701

c m - 1 ,

r espec t ive ly. The o rder o f ip and op

v(C=C)2 i s r ever s ed when compar ing i t to thos e fo r the 2 , 5 -norbornad ienes .

The ip and op c i s (CH= CH )2 w ag occur a t 748 and 6 58 cm -1 fo r 1 , 3 -cyc lohexad iene ,

r espec tive ly . In the cas e o f the 1 , 5 -no rbornad ien es ip and op c i s (C H= CH ) wag occ ur a t 654 and

7 2 8 - 7 3 5 c m - 1 , r es pec t ive ly . Aga in the ip and op c i s (CH=CH wag) mode as s ignmen ts a r e in the

rever s e o rde r fo r thes e two s e t s o f compounds .

A L K Y L G R O U P S O F 1 - A L K E N E S A N D V I N Y L A L K Y L

E T H E R S

Tab le 4 .17 con ta ins the IR vapor -phas e da ta and as s ignm en ts fo r the ca rbon hyd roge n v ib ra t ions

fo r the 1 -a lkenes ( a ls o s ee Tab le 4 .1 ) . Thes e as s ig nme n ts a r e g iven he re r a the r than in C hap te r 3

fo r the conven ience o f thos e in te r es ted in the v ib ra t iona l s pec t r a o f 1 -a lkenes .

Tab le 4 . 18 con ta ins the IR vapor -phas e da ta and as s ignm en ts fo r the a lky l g roup o f v iny l a lky l

e the r s ( a l s o s ee Tab le 4 . 2b ) . The as s ignmen ts a r e p laced he re r a the r than in Chap te r 3 fo r the

conven ien ce o f thos e in te r es ted in the v ib ra t iona l s pec t r a o f v iny l a lky l e the r s .

R E F E R E N C E S

1. Nyquist, R. A. (1989). The Infrared Spectra, Bui lding Blocks of Polymers, Philadelphia: Sadtler Research Laboratories.

A Div ision of Bio-Rad.

2. Ny quist, R. A. (1984). The Interpretation of Vapor-Phase Infrared Spectra: Grou p Frequency Data , Philadelphia: Sadlter

Research Laboratories, A Division of Bio-Rad.

3. Ny quist, R. A. (ed.) (1984).

A Collection of 9200 Spectra,

Philadelphia: Sadtler Standard Infrared Vapor Phase Spectra,

Sadtler Research Laboratories, A Division of Bio-Rad.

4. (1987). Sadlter Standard Raman Spectra, Philadelphia: Sadtler Research Laboratories, A Division of Bio-Rad.

5. Potts, W. J. and N yquis t, R. A. (1959). Spectrochim. Acta, 15, 679.

6. Owen, N. L. and Sheppard, N. (1964). Trans, Faraday S oc. , 60, 634.

7. McLachlan, R. D. and Nyquist, R. A. (1968). Spectrochim. Acta, 24A, 103.

8. Nyquist, R. A. (1992). App l. Spectrosc. , 47, 560.

9. Colth up, N. B. , Daly, L. H. , and Wiberley, S. E. (1990).

Introduction to Infrared and Ram an Spectroscopy,

3rd ed. , New

York: Academic Press.

10. Lin-Vien, D. , Colth up, N. B. , Fateley, W. G. , and Grasselli , J. G. (1991). The Handbook of Infrared and Raman

Frequencies of Organic Molecules, Boston: Academic Press, Inc.

11. Nyquist, R. A. and Streck, R. (1994). Vib. Spectrosc., 8, 71.

12. Nyquist, R. A. (1986). App l. Spectrosc. , 40, 196.


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Var iab les in Data In te rpre ta t ion 69

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16/37

70 A lkenes and O the r C om pounds C on ta in ing C - -C D oub le B onds

Viny l CH2 Wag Frequencies For Styrene And Substituted Styrenes

Vs. pKe Value s For P henol And C orresponding Subs tituted Phenols.

Viny l CH2 Wag

9 4 0 -

cm 1

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9 2 5

9 2 0

9 1 5

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9 Styrene Substituted W ith Atoms Or G roups

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_

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5 6 7 8 9 1 0 11

pK,

FIGUR E 4.3 P lots of the C=CH 2 wag f requencies for s tyrenes and r ing subst i tuted s tyrenes vs the pKa values for

correspondingly subst i tuted phenols .

( V i n y l T w i s t ) - ( V i n y l C H 2 W a g)

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I_C4_Alkenes and other compounds containing C=C double bonds.pdf

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