11ALKENESALKENES are hydrocarbons:

* with C=C bonds;

* of general formula CnH2n;

* having 120° bond angles and trigonal planar shape

around the C= ;

22Examples:Examples:

ethylene H H

C=C

H H

H CH3

C=C

H H

propene

33A C=C is made up of 2 types of bonds:

The The bond is a standard C-C. bond is a standard C-C.

The bond is weaker than .

Overall, the C=C is stronger Overall, the C=C is stronger (but not 2x stronger) and (but not 2x stronger) and shorter than a C-C.shorter than a C-C.

44Naming alkenes1. Find longest chain of C that 1. Find longest chain of C that

contains the C=C.contains the C=C.

2. Number chain to give one 2. Number chain to give one of of the C in C=C the lowest the C in C=C the lowest possible locant.possible locant.

3. Change name of parent 3. Change name of parent alkalkaane to alkne to alkeene.ne.

554. Give the lower locant 4. Give the lower locant

number for a C=C in front number for a C=C in front of of the parent alkene name.the parent alkene name.

5. Number and name other 5. Number and name other substituents as usual.substituents as usual.

66Example

CH3-CH-CH2-CH-CH=CH-CH3

Br CH2CH3

7 carbons in chain= hept7 carbons in chain= hept

ending = eneending = ene

# from right = 2-heptene# from right = 2-heptene

77

CH3-CH-CH2-CH-CH=CH-CH3

Br CH2CH3

7 6 5 4 3 2 17 6 5 4 3 2 1

bromobromo ethylethyl

complete name =

6-bromo-4-ethyl-2-heptene6-bromo-4-ethyl-2-heptene

88Naming cycloalkenes1. Start numbering of ring C 1. Start numbering of ring C at at one of the C in C=C.one of the C in C=C.

2. Position #2 is the second C 2. Position #2 is the second C of the of the C=C.C=C.

3. Count in the direction 3. Count in the direction which which gives other gives other substituents substituents the lower the lower set of locant #.set of locant #.

99Example

CH2CH3

Br

11

22

33

44

complete name=

4-bromo-3-ethylcyclohexene4-bromo-3-ethylcyclohexene

1010Stereoisomers are:* isomersisomers (= same formula),* having same constitution having same constitution (=same kinds & sequence of bonds),* but permanently different but permanently different arrangements of groups in arrangements of groups in space.space.

1111Stereoisomers are of several types, depending on what phenomenon causes them to exist.

Geometric isomers Geometric isomers are stereoisomers because of restricted rotation around bonds (C-C or C=C).

1212In alkenes the two bonds between the C of the C=C prevents free rotation of the groups around the C=C bond.

ciscis and transtrans geometric isomers have different physical and chemical properties: they are distinctly different compounds.

1313Compare the corresponding alkenes:

H H CH3 H

C=C C=C

CH3 CH3 H CH3

cis-2-butenecis-2-butene trans-2-trans-2-butenebutene

1414When can an alkene exist as geometric isomers?==> the same C of C=C must ==> the same C of C=C must have two different groups bonded have two different groups bonded to it.to it.

CHCH33CHCH22 H H

C=C C=C 1-butene: no1-butene: no H H H H cis or trans cis or trans

1515

CH3

CH3

C=CH

CH2CH3

2-methyl-2-pentene

has no geometric isomer

1616Addition Reactions are typical of alkenes.

General schematic equation:General schematic equation:

C=C + C=C + XX--YY ----> ---->

C-CC-C

XX YY

1717In an addition reaction:

* the * the bond of C=C “breaks” bond of C=C “breaks”

* the covalent bond between X,Y * the covalent bond between X,Y “breaks”“breaks”

* new C-X and C-Y * new C-X and C-Y bonds bonds formform

1818

When bonds break and form in reactions, the shared electron pairs are scrambled or rearranged ... to be shared by different atoms.

1919In the addition reaction, X and Y can be the same element or different elements.

Examples of X=YExamples of X=Y

HH22, Cl, Cl22, Br, Br22

Example of X, Y DifferentExample of X, Y Different

HH22O written as H-OHO written as H-OH

2020CH3-CH=CH2

HH22, Pt(metal catalyst)

CH3CH-CH2 = CH3CH2CH3

H H

2121

so, the general equation is:

alkene + Halkene + H22 --> alkane --> alkane

This process is called catalytic reduction or hydrogenation because the H2 is added with the help of a catalyst.

2222

HOH (water) alone does not react with an alkene – it requires a catalyst. Addition of water to the alkene C=C is called hydration .

In lab the catalyst is H+ (acid), often from H2SO4.

In a living cell the catalyst is an enzyme.

2323When alkene is symmetrical, one addition product forms: H+

CH3-CH=CH-CH3 + HH-OH OH --->--->

CHCH33-CH-CH-CH-CH-CH-CH33 CHCH33-CH-CH-CH-CH-CH-CH3 3

HH OH OH OH OH HH

either way, same product either way, same product

2424If alkene is unsymmetrical:

CH3-CH=CH2 + HH-OH OH + H+ H++ --->

CH3-CH-CH2 ONLY!ONLY!

OHOH HH

NONE of this forms:NONE of this forms:

CH3-CH-CH2

HH OHOH

2525

Markovnikov found:

“when HH-XX adds to a C=C of alkene, HH attaches to the C of C=C that already had more H bonded to it.”

HH-XX =

HH-ClCl, HH-BrBr, HH-II, HH-OHOH

2626Example:

CH3CH2CH=CH2 + H2O ---->

CH3CH2CH-CH2

OH H

more commonly written as

CH3CH2CH-CH3

OH

H+

2727

Alkynes are hydrocarbons that:

* contain a C* contain a CCC

* have general formula C* have general formula CnnHH2n-22n-2

* have linear geometry, 180° * have linear geometry, 180° bond bond angleangle

2828Examples of Alkynes

H-C C-H AcetyleneAcetylene

CH3CH2-C C-H 1-butyne, a terminal

alkyne

CH3-C C-CH3 2-butyne, an internal

alkyne

2929Naming Alkynes:Naming Alkynes:1. find longest chain that 1. find longest chain that

includes C C.includes C C.2. change parent name of 2. change parent name of longest chain from longest chain from “alk“alkaane” to “alkne” to “alkyyne.”ne.”3. give lowest possible locant # 3. give lowest possible locant # to the to the first C of C C.first C of C C.4. locate other substituents as 4. locate other substituents as usual.usual.

3030Naming example

Cl

CH3CH-CH-CH2-C C-CH3

CH3

6-chloro-5-methyl-2-heptyne6-chloro-5-methyl-2-heptyne

3131Aromatic Compounds:* usually contain six double-* usually contain six double-bondedbonded carbon atoms in a carbon atoms in a ring;ring;

* have alternating C-C & C=C;

* have a flat ring structure;* have a flat ring structure;

* do NOT undergo addition reactions like alkenes.

3232Ways to draw aromatic ring:

or or

Each vertex = C; each C in ring can have one more bond. If no connection shown, bond is to H.

3333Some important aromatic compounds:

CH3 NH2 OH

benzene aniline

toluene

phenol

3434

When a benzene ring is a substituent on a parent chain, it is called “phenyl” :

CH3CH=CCH2CH2CH2CH2CH3

3-phenyl-2-octene