Chemistry Unit 4 Goodie bag

35
A2 CHEMISTRY UNIT 4: IDENTIFYING ORGANIC COMPOUNDS 1. A compound containing 58.8% carbon, 9.8% hydrogen and 31.4% oxygen is subjected to mass spectrometry and found to give intense peaks at m/z = 43 and m/z = 57, in addition to a molecular ion peak at m/z = 102. Infra-red analysis of the molecule showed a sharp peak at m/z = 1710 cm -1 . A proton nmr spectrum of the molecule yielded the following peaks: Chemical shift Splitting Integratio n factor 0.8 Triplet 3 1.1 Sextet 2 2.3 Triplet 2 3.7 Singlet 3 Deduce the structure of the molecule and account for the formation of all the peaks the spectra. 2. This question concerns four isomers, W, X, Y and Z, with the molecular formula C 5 H 10 O 2 1

Transcript of Chemistry Unit 4 Goodie bag

Page 1: Chemistry Unit 4 Goodie bag

A2 CHEMISTRY UNIT 4: IDENTIFYING ORGANIC COMPOUNDS

1. A compound containing 58.8% carbon, 9.8% hydrogen and 31.4% oxygen is subjected to mass spectrometry and found to give intense peaks at m/z = 43 and m/z = 57, in addition to a molecular ion peak at m/z = 102.

Infra-red analysis of the molecule showed a sharp peak at m/z = 1710 cm-1.

A proton nmr spectrum of the molecule yielded the following peaks:

Chemical shift Splitting Integration factor

0.8 Triplet 31.1 Sextet 22.3 Triplet 23.7 Singlet 3

Deduce the structure of the molecule and account for the formation of all the peaks the spectra.

2. This question concerns four isomers, W, X, Y and Z, with the molecular formula C5H10O2

(a) The proton n.m.r. spectrum of W shows 4 peaks.The table below gives the chemical shifts, δ values, for each of these peaks, together with their splitting patterns and integration values.

δ/ppm 2.18 2.59 3.33 3.64

Splitting pattern singlet triplet singlet triplet

Integration value 3 2 3 2

1

Page 2: Chemistry Unit 4 Goodie bag

State what can be deduced about the structure of W from the presence of the following in its n.m.r. spectrum.

(i) The singlet peak at δ = 2.18

..................................................................................................

(ii) The singlet peak at δ = 3.33

................................................................................................

(iii) Two triplet peaks.

.................................................................................................

(iv) Hence, deduce the structure of W.

(b) The infra-red spectrum of X is shown below.

1 0 0

5 0

0

Tra

nsm

itta

nce/

%

4 0 0 0 3 0 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0

W av en u m b er/cm – 1

(i) What can be deduced from the broad absorption centred on 3000

cm–1 in the infra-red spectrum of X?

............................................................................................................

2

Page 3: Chemistry Unit 4 Goodie bag

(ii) Given that the proton n.m.r. spectrum of X contains only two peaks with the integration ratio 9:1, deduce the structure of X.

(c) Isomers Y and Z have the structures shown below.

C H 3

C H 3

CC

O

H C O H3

Y

C

O

H C3 C H C O H

C H 3

H

Z

2

Identify the two reagents you could use in a simple chemical test to distinguish between Y and Z. State what you would observe when each of Y and Z is tested with a mixture of these two reagents.

Reagents ....................................................................................................

Observation with Y .....................................................................................................

.

Observation with Z.....................................................................................................

.

3. Compounds C and D, shown below, are isomers of C5H10O

H C C C H C H C H

O

2 2 33

2

2

2

2

H C

H CC

C

C

H

H

H

O H

C D

(a) Name compound C.

.....................………………………………………………………………

3

Page 4: Chemistry Unit 4 Goodie bag

(b) Use the Data book to help you to answer this question.

(i) Suggest the wavenumber of an absorption which is present in the infra-red spectrum of C but not in that of D.

...........……………………………………………………………………

(ii) Suggest the wavenumber of an absorption which is present in the infra-red spectrum of D but not in that of C.

...........……………………………………………………………………

(c) Deduce the number of peaks in the proton n.m.r. spectrum of C.

.....................…………………………………………………………………

(d) Identify a reagent that you could use to distinguish between C and D. For each of C and D, state what you would observe when the compound is treated with this reagent.

Reagent ……………………………..………………………………………………..

Observation with C …………………………………………………………………..

Observation with D …………………………………………………………………..

(e) Compound E, CH3CH2CH2CH2CHO, is also an isomer of C5H10O

Identify a reagent which will react with E but not with C or D. State what you would observe when E is treated with this reagent.

Reagent ……………………………..………………………………………………..

Observation with E …………………………………………………………………..

4

Page 5: Chemistry Unit 4 Goodie bag

4. Each of the parts (a) to (e) below concerns a different pair of isomers.

Draw one possible structure for each of the species A to J, using your data book to help you

(a) Compounds A and B have the molecular formula C5H10

A decolourises bromine water but B does not.

A B

(b) Compounds C and D have the molecular formula C2H4O2

Each has an absorption in its infra-red spectrum at about 1700 cm–1 but

only D has a broad absorption at 3350 cm–1

C D

5

Page 6: Chemistry Unit 4 Goodie bag

(c) Compounds E and F are esters with the molecular formula C5H10O2

The proton n.m.r. spectrum of E consists of two singlets only whereas that of F consists of two quartets and two triplets.

E F

(d) Compounds G and H have the molecular formula C3H6Cl2 G shows optical activity but H does not.

G H

(e) Compounds I and J have the molecular formula C6H12

Each has an absorption in its infra-red spectrum at about 1650 cm–1 and neither shows geometrical isomerism. The proton n.m.r. spectrum of I consists of a singlet only whereas that of J consists of a singlet, a triplet and a quartet.

I J

6

Page 7: Chemistry Unit 4 Goodie bag

5. The proton n.m.r. spectrum of an organic compound F, C4H8O, is shown below.

3 2 1 0/p p m

The measured integration trace gives the ratio 0.5 to 0.75 to 0.75 for the peaks at δ 2.47 (quartet), δ 2.15 and δ 1.05 (triplet), respectively. The infra-red spectrum of

compound F has an intense band at 1715 cm–1. In the mass spectrum of F, dominant fragmentation peaks appear at m/z = 43 and m/z = 57.

(a) Give the structural formula of the compound responsible for the signal at δ 0.00 in the n.m.r. spectrum.

7

Page 8: Chemistry Unit 4 Goodie bag

(b) How many different types of proton are present in compound F?

....................................................................................................................

(c) What is the ratio of the numbers of each type of proton?

...................................................................................................................

(d) Which alkyl group is responsible for the signal at 2.15 in the n.m.r. spectrum?

....................................................................................................................

(e) The peaks at δ 2.47 and δ 1.05 arise from one group in compound F. Identify this group and explain the appearance of the splitting pattern shown in the n.m.r. spectrum.

Group..........................................................................................................

Explanation ................................................................................................

....................................................................................................................

...................................................................................................................

(f) Which group is responsible for the band at 1715 cm–1 in the infra-red spectrum of compound F?

...................................................................................................................

(g) Give the structures of the species responsible for the peaks at m/z values of 43 and 57 in the mass spectrum.

Peak at m/z = 43.........................................................................................

Peak at m/z = 57.........................................................................................

(h) Give the structure of compound F.

...................................................................................................................

8

Page 9: Chemistry Unit 4 Goodie bag

6. (a) Describe how propanal, CH3CH2CHO, and propanone, CH3COCH3, can be distinguished using

(i) a chemical test

(ii) the number of peaks in their proton n.m.r. spectra.

(b) Compound Z can be produced by the reaction of compound X with compound Y as shown in the synthesis outlined below.

C H C H C H OS te p 1

S te p 2C H C O C H

C H C H C

O

O C H

C H

C H

3

3

3 3

3 2

2

3

S te p 3

X

YZ

i) Identify compounds X and Y. For each of the three steps in the synthesis, name the type of reaction involved and give reagents and conditions.

9

Page 10: Chemistry Unit 4 Goodie bag

7. The proton n.m.r. spectrum of compound X is shown below.

4.3

4.2

4.1

4.0

3.9

3.8

3.7

3.6

3.5

3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

2.5

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

Che

mic

al s

hift

, /p

pm

10

Page 11: Chemistry Unit 4 Goodie bag

Compound X, C7H12O3, contains both a ketone and an ester functional group. The measured integration trace for the peaks in the n.m.r. spectrum of X gives the ratio shown in the table below.

Chemical shift, δ/ppm 4.13 2.76 2.57 2.20 1.26

Integration ratio 0.8 0.8 0.8 1.2 1.2

Answer the following questions.

(a) How many different types of proton are present in compound X?

...............................................................................................................................

(b) What is the whole-number ratio of each type of proton in compound X?

...............................................................................................................................

(c) Draw the part of the structure of X which can be deduced from the presence of the peak at δ2.20.

...............................................................................................................................

(d) The peaks at δ4.13 and δ1.26 arise from the presence of an alkyl group. Identify the group and explain the splitting pattern.

Alkyl group ...........................................................................................................

Explanation ...........................................................................................................

...............................................................................................................................

...............................................................................................................................

(e) Draw the part of the structure of X which can be deduced from the splitting of the peaks at δ 2.76 and δ 2.57.

...............................................................................................................................

(f) Deduce the structure of compound X.

...............................................................................................................................

11

Page 12: Chemistry Unit 4 Goodie bag

8. Compound Q has the molecular formula C4H7ClO and does not produce misty fumes when added to water.

(a) The infra-red spectrum of Q contains a major absorption at 1724 cm–1. Identify the bond responsible for this absorption.

....................................................................................................................

(b) The mass spectrum of Q contains two molecular ion peaks at m/z = 106 and m/z = 108.It also has a major peak at m/z = 43.

(i) Suggest why there are two molecular ion peaks.

............................................................................................................

(ii) A fragment ion produced from Q has m/z = 43 and contains atoms of three different elements. Identify this fragment ion and write an equation showing its formation from the molecular ion of Q.

Fragment ion ......................................................................................

Equation..............................................................................................

(c) The proton n.m.r. spectrum of Q was recorded.

(i) Suggest a suitable solvent for use in recording this spectrum of Q.

............................................................................................................

(ii) Give the formula of the standard reference compound used in recording proton n.m.r. spectra.

............................................................................................................

(d) The proton n.m.r. spectrum of Q shows three peaks. Complete the table below to show the number of adjacent, non-equivalent protons responsible for the splitting pattern.

Peak 1 Peak 2 Peak 3

Integration value 3 3 1

Splitting pattern doublet singlet Quartet

Number of adjacent,non-equivalent protons

1

12

Page 13: Chemistry Unit 4 Goodie bag

(e) Using the information in parts (a), (b) and (d), deduce the structure of compound Q.

(f) A structural isomer of Q reacts with cold water to produce misty fumes. Suggest a structure for this isomer.

9. Compound Q has the molecular formula C4H8O2

(a) The infra-red spectrum of Q is shown below.

1 0 0

5 0

04 0 00 3 0 0 0 2 0 0 0 1 5 00 1 0 0 0 5 0 0

W a ve n u m b e r/cm

Tra

nsm

ittan

ce/%

R S

– 1

Identify the type of bond causing the absorption labelled R and that causing the absorption labelled S.

R .................................................................................................................

S ................................................................................................................

13

Page 14: Chemistry Unit 4 Goodie bag

(b) Q does not react with Tollens’ reagent or Fehling’s solution. Identify a functional group which would react with these reagents and therefore cannot be present in Q.................................................................................................................

(c) Proton n.m.r. spectra are recorded using a solution of a substance to which tetramethylsilane (TMS) has been added.

(i) Give two reasons why TMS is a suitable standard.

Reason 1 ............................................................................................

Reason 2 ...........................................................................................

(ii) Give an example of a solvent which is suitable for use in recording an n.m.r. spectrum. Give a reason for your choice.

Solvent ...............................................................................................

Reason ...............................................................................................

(d) The proton n.m.r. spectrum of Q shows 4 peaks.

The table below gives δ values for each of these peaks together with their splitting patterns and integration values.

δ/ppm 2.20 2.69 3.40 3.84

Splitting pattern singlet triplet singlet triplet

Integration value 3 2 1 2

What can be deduced about the structure of Q from the presence of the following in its n.m.r. spectrum?

(i) The singlet peak at δ = 2.20

...........................................................................................................

(ii) The singlet peak at δ = 3.40

...........................................................................................................

(iii) Two triplet peaks

...........................................................................................................

(e) Using your answers to (a), (b) & (d),deduce the structure of compound Q.

14

Page 15: Chemistry Unit 4 Goodie bag

10. The proton n.m.r. spectrum of an ester, A, is shown below.

4 3 2 1

Chemical shift, δ/ppm

The measured integration trace gives the ratio 0.50 to 0.50 to 0.75 to 0.75 for the peaks at δ 4.13, 2.32, 1.33 and 1.09, respectively.

(a) The mass spectrum of compound A has a molecular ion peak at m/z = 102. Deduce the molecular formula of compound A.

...................................................................................................................

15

Page 16: Chemistry Unit 4 Goodie bag

.....................................................................................................................................

.....................................................................................................................................(3)

(b) What is the ratio of the numbers of each type of proton?

.....................................................................................................................................(1)

(c) What can be deduced about the arrangement of protons from the splitting patterns in the n.m.r. spectrum?

.....................................................................................................................................(1)

(d) Deduce the structure of compound A and label with the letters a, b, c and d the four groups of equivalent protons.

(1)

(e) Assign the various signals in the table below to the groups of protons in compound A previously labelled a, b, c and d.

Chemical shift, /ppm 1.09 1.33 2.32 4.13

Label of group

(4)

16

Page 17: Chemistry Unit 4 Goodie bag

11. Each of the parts (a) to (f) below concerns a different pair of isomers. Deduce one possible structural formula for each of the species A to L.

(a) A and B have the molecular formula C2H4O2. An aqueous solution of A reacts with calcium carbonate to liberate carbon dioxide, but B does not.

A B

(b) C and D have the molecular formula C3H8O. C has a broad absorption

band at 3300 cm–1 in its infra-red spectrum, but D does not.

C D

(c) E and F have the molecular formula C3H6C12. E has only one peak in its low resolution proton n.m.r. spectrum but F has two.

E F

17

Page 18: Chemistry Unit 4 Goodie bag

(d) G and H have the molecular formula C3H6O and both have strong

absorption bands at about 1700 cm–1 in their infra-red spectra. G turns acidified potassium dichromate(VI) solution green but H does not.

G H

(e) I and J have the molecular formula C4H9Br. I shows optical activity, but J does not.

I J

(f) K and L have the molecular formula C5H10. K has a weak absorption

band at 1650 cm–1 in its infra-red spectrum, but L does not.

K L

18

Page 19: Chemistry Unit 4 Goodie bag

ANSWERS

1. Molecular formula = C5H10O2

infra-red spectrum:peak at 1710 cm-1 indicates a carbonyl

proton nmr spectrum:peak at 0.8 is CH3- adjacent to -CH2-peak at 1.1 is -CH2- adjacent to CH3- and -CH2-peak at 2.3 is -CH2CO- adjacent to -CH2-peak at 3.7 is CH3O- so molecule is methyl butanoate, CH3CH2CH2COOCH3

mass spectrum:peak at 43 from: CH3CH2CH2COOCH3

+. CH3CH2CH2+ + .COOCH3

peak at 57 from: CH3CH2CH2COOCH3+. CH3CH2CH2CO+ + .OCH3

2. (a) (i)

CH C

O

3

or RCOCH3; 1

(ii) H3C—O or ROCH3; 1

(iii) CH2CH2 or two adjacent methylene groups; 1

(iv)

C H -C C H -C H -O C H

O

3 2 32

OR

CH3COCH2CH2OCH3; 1

(b) (i) OH in acids or (carboxylic) acid present

(ii)

C H

CC H

C H

C O O H

3

3

3

(c)

reagentK2Cr207 /H

+

Y no reaction

Z orange to green or turns green

5

3. (a) Pentan-2-one 1

19

Page 20: Chemistry Unit 4 Goodie bag

(b) (i) 1680 – 1750 (cm–1

) 1

(ii) 3230 – 3550 (cm–1

) 1

(c) 4

(d)Reagent K2Cr2O7/

H+

Na CH3COOH/

H2SO4

1

with C no reaction no reaction no reaction 1with D goes green effervescence Sweet smell 1

(e)Reagent Tollens Fehlings or Benedicts 1with E silver

(mirror)red ppt or goes red(not red solution)

1

4. (a) A any C5 alkene 1

B

e tcp en a lise

H 2

H 2

H 2

H 2H 2 1

(b) C

H C3 CO

O H o r

H CO

O C H 3 1

or CH3COOH or HCOOCH3

D

H C2

O H

CH

O1

or HOCH2CHO

(c) E

H CO

O C C H 3

C H 3

C H 3

1

20

Page 21: Chemistry Unit 4 Goodie bag

F

C H C H CO

O C H C H2

3 2

3 (a llo w C H )2 5 1

(d) GH

C

C l

H C3 C H C l2

1

HH

C

H

H C3 C H C l 2

H

C

H

C lH C C H C l22

C l

C

C l

H C C H 33o ro r

1

(e) IH C3

H C3

C CC H 3

C H 3 1

JH

HC C

C H C H2

C H C H2

3

3 (a llo w C H )2 5 NOT hex-3-ene 1[10]

5. (a) (CH3)4Si (1) 1

(b) 3 (1) 1

(c) 2 : 3 : 3 (1) 1

(d) methyl or CH3 (1) 1

(e) Group ethyl or CH2CH3 or C2H5 (1)

Explanation CH3 splits CH2 quartet or 4 peaks (1)

CH2 splits CH3 triplet or 3 peaks (1) 3

(f) C = O (1) 1

(g) Peak at m/z = 43 CH3CO+

or [CH3CO]+

(1)

Peak at m/z = 57 CH3CH2CO+

or [CH3CH2CO]+

(1) 2

21

Page 22: Chemistry Unit 4 Goodie bag

(h) CH3COCH2CH3 (1) 1

[11]

6. (a) (i)

Reagent Tollens Fehlings or BenedictsK2Cr2O7/H

+

or acidified

I2/Na0H

Propanal silver (mirror)

red ppt or goes red(not red solution)

goes green Noreaction

Propanone no reaction

no reaction no reaction Yellow(ppt)

(penalise incomplete reagent e.g. K2Cr2O7 or Cr2O72–

/H+

then mark on)

3

(ii) propanal 3 peaks ignore splitting even if wrong 1propanone 1 peak 1

(b) X is CH3CH2COOH or propanoic acid if both name and formula given, 1

both must be correct, but

Y is CH3CH(OH)CH3 or propan-2-ol allow propanol with correct formula 1

Mark the type of reaction and reagent/condition independently.The reagent must be correct or close to score condition

Step 1 Oxidation 1

K2Cr2O7/H+

or other oxidation methods as above

allow Cr2O72–

H+

if penalised above (ecf)

reflux (not Tollens/Fehlings) or heat or warm

Step 2 reduction or nucleophilicaddition

reduction ornucleophilic addition

reduction or hydrogenation

1

NaBH4 LiAlH4 H2 1

in (m)ethanol or water or etheror dry

ether or dry Ni / Pt etc 1

22

Page 23: Chemistry Unit 4 Goodie bag

Step 3 esterification or (nucleophilic) addition-elimination or condensation 1(conc) H2SO4 or HCl 1

warm (allow without acid reagent if X and Y given as reagents) 1or reflux or heat 1

[15]

7. (a) 5 (1) 1

(b) 2:2:2:3:3 (1)any order but not multiples

1

(c)3C H

O

C (R ) (1) 1

(d) CH3CH2 or C2H5 or ethyl (1)

4.13 (quartet) : CH2 peak split by CH3 / next to CH3 (1)

1.26 (triplet) : CH3 peak split by CH2 / next to CH2 (1) 3

(e) CH2CH2 (1) 1

(f) 3 32 2 2O C H C HCC H C HCC H

OO

(C O ) (C O )(2)

allow (1) for CH3COCH2OCOCH2CH3or CH3COOCH2COCH2CH3

Must be C7H12O3

8. (a) C=O (1) 1or “carbonyl”

(b) (i) Cl has (2) isotopes (1)

Allow 35

Cl and 37

Cl without word isotope – but must be correct isotopes

must have 3 different elements, i.e. not C3H7+

but allow balanced

equation including C3H7+

for the equation mark

(ii) Fragmentation: OCCH3

(1)

must be an ion (*)

23

Page 24: Chemistry Unit 4 Goodie bag

Equation: C4H7ClO+ OCCH3

+ C2H4Cl (1) 3

(*) allow C2H3O+ or any form of it (i.e. CH2CHO+

or CH2COH+

)

in equation, be generous with position of + or if fragment ion completely wrong (not m/z = 43) no further marks

(c) (i) CDCl3 or CCl4 (1) or D2O, C6D6

(ii) Si(CH3)4 (1) or SiC4H12 2

(d)

Peak 1 Peak 2 Peak

Integration value 3 3 1

Splitting pattern doublet singlet quartet

Number of adjacent, non-equivalent protons

1 0 3

(1) 1

(e)C H C C H C H

O C l

3 3 (1) 1

or CH3COCHClCH3

(f)

C H C H C H C o r (C H ) C H C O C lO

C l3

3 2 2

32 22

o r

C H C H C H C O C l

(1) 1

9. (a) R: O-H (alcohols) (1)

S: C=O or carbonyl (1)

2

(b) aldehyde (1) -CHO or RCHO (1)

1

(c) (i) Reason 1: TMS inert or non-toxic or volatile / easily removedReason 2: single (intense) peak

peak of 12 protons

24

Page 25: Chemistry Unit 4 Goodie bag

has 12 equivalent protons all protons in same environment

OR peak / signal upfield of others highly shielded more shielded peak away from others or = 0 or low

not solvent, not cheap

any 2 reasons × (1)

(ii) Solvent: CDCl3 or CCl4 (NOT D2O)

Reason: proton free (1) allow no hydrogens (atoms)

NOT H+

/ hydrogen ions

4

(d) (i)CC H

O

3 (1)

(ii) –OH (1)

(iii) –CH2–CH2– (1) 3

(e)CC H C H C H O H

O

3 2 2 (1) 1

10. (a) A is RCOOR (1)

R + R = 102 – 44 = 58 (1) C4H10

C5H10O2 (1) 3

(b) 2 : 2 : 3 : 3 (1) 1

(c) Two CH2CH3 groups present (1) 1

(d) Ca

3H C2

b

H COOCc

2H C3

d

H (1) 1

(e)

Chemical shift, /ppm 1.09 1.33 2.32 4.13

Label of group a (1) d (1) b (1) c (1)

25

Page 26: Chemistry Unit 4 Goodie bag

4

11. (a) A B

CH3COOH (1) HCOOCH3

or HOCH2CH

O(1) 2

(b) C D

CH3CH2CH2OH CH3CH2–O–CH3 (1)

or CH3CH(OH)CH3 (1) 2

(c) E F

C

C l

C l

C H C H3 3

(1 )

C H

C l C l

C H C H2 2 2

(1) 2

(d) G H

CH3CH2CHO (1) CH3COCH3 (1) 2

(e) I J

C

B r

H

C H C H C H3 2 3

(1 ) (1 )

C H 3

3

3 3

2 2

C H 2 C H 2 C H 2 B ro r (C H ) C H C H B ro r (C H ) C B r

2

(f) K Lone alkene e.g. one cycloalkane e.g.C H = C H C H C H C H22 2 3

C H – C H = C H – C H C H3 2 3

(C H ) C = C H C H3 2 3

H C = C (C H )C H C H32 2 3

(1 )

e tc

C H

C H

C H

C H C H

3

3

3

2 3

(1 )

26