Chapter 12 Alkenes, Alkynes, and Aromatic Compounds

Compounds with multiple bonds

The most important compound with a triple bond

is ethyne also known as acetylene;

it is used in the oxy acetylene torch.

Bombykol, is another natural product that contains double bonds. We will examine the structure of these materials shortly

Compounds of carbon and hydrogen with less tha 2n+ 2 hydrogens other than cyclic hydrocarbons

Is there any other way of satisfying the octet for carbon in a molecule with a formula C2H4 or C2H2?

HC

HC

H

H::

How many groups around each C? (bonding electrons are not considered to be a group)

3

What’s the geometry? triangular

How about C2H2?

CH HC≡ How many groups around each C? 2

What’s the geometry? linear

ethene or ethylene

What does ethylene have to do with fruit?

A systematic way of naming alkenes and identifying identical structures

1. Locate the longest carbon chain in the molecule that contains the double bonds: this identifies the parent alkene

2. Identify the points of branching and count the number of carbons in each branch; name the alkyl branches in the normal way: methyl, ethyl ...

3. Give the double bond the lowest number

4. Identify any stereochemistry

CH2CCH2

CH2 CH3

CH3

parent: groups:location:

4 carbons: butene2 carbons: ethyldouble bond at position 1; ethyl at 2

2-ethyl-1-butene no stereochemistry to describe

All these formulas for butane are identical because of rapid rotation about C-C bonds

no, rotation about C=C bonds does not occur

Are these two compounds the same?

If the two groups are on the same side of the double bond, use cis

On opposite sides, use trans

H2C

H2CCH2

CH

CH2

CH

CH2-CH3

Cl

parent: cyclohexanegroups: ethyl, chlorolocation: 1, 3

CH2CH3

Cl

CH2CH3

Cl

The solid wedge is used to denote a group sticking out of the plane of the screen

A dotted wedge is used to denote a group sticking out of the plane of the screen

Two groups with the same relative orientation is called cis

Two groups with the opposite relative orientation is called trans

Naming compounds with double and triple bonds

generic names alkane

alkene

alkyneCC HH

CH2H2C

CH3H3C ethane

ethene or ethylene

ethyne or acetylene

CC CH3CH3

CH3

CH3

H

H

H

CH3

H

CH3 cis 2-butene

trans 2-butene

2-butyne

CH2CH3

HH

H

CC CH2CH3H

1-butene

1-butyne

CCCH2CH3

HH

H

Name the following: CCH

CH2CH2CH2CH3H

CH

CH3

CH3CH2

parent: groups:location:

nonenemethyl, double bond

3-methyl, 4-double bond

trans 3-methyl-4-nonene

H2C

H2CCH2

CH

CHC

H CH3

shorthand notation

parent: groups:location:

cyclohexenemethyl

1, 3 or 1,2?

3-methyl-1-cyclohexene or

1-methyl-2-cyclohexene

stereochemistry: trans

A pheromone is a chemical messenger emitted by insects in minute quantities.

Bombykol is emitted by the silkworm moth to attract other moths and has one cis and one trans double bond

16 C: hexadecane parent alkane

2 double bonds diene

alcohol: drop the last e and add ol

stereochemistry: cis and trans(CH2)7 means 7 CH2 groups in a row

To name this compound we need to know how to name a compound with 16 carbon atoms

How to name compounds with more than one double bond

How to name alcohols and how to designate “stereochemistry” (the arrangement of groups in space:

trans10, cis 12-hexadecadien-1-ol

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

parent:groups:locationstereochemistry:

parent: groups:location:stereochemistry:

Name the following:

cis-1,2-Dibromoethene

trans-2-Butene

1,1-Dichloropropene

parent: groups:location: stereochemistry:

ethenebromo1,2cis

butenedouble bond2trans

propenechloro1,1none

CH3

CCH2

CH2

CH3CH

CH3 CH

CH2

C

CH2

CH3

parent:groups:locationstereochemistry:

parent:groups:locationstereochemistry:

C

C

C

C

CH3

Basic carbon framwork of many natural products

C

CCH

CH2

CC

CH3

CHCH3

CH3

H H

H

DillAnethum graveolens (Umbelliferae)Dill is a thin, annual originating in the Middle East. Since recorded history it has been cultivated as a medicinal and aromatic herb. It was spread through Europe by way of the monasteries. The picture on the left shows a 'broad-leafed' variety, the original type has completely thready leaflets. The fresh dill leaves and flowers contain an essential oil whose main component is (-)-alpha-phellandrene (ca. 60 %).

2 -methyl-5-isopropyl-1,3-cyclohexadiene

CHCH2

CHCH3CH3

HC

C

CC

CH3

H

H

Draw structures for the following compounds:

1-hexyne

2-methyl-1,7-octadiene

1,2-propadiene

Compounds of carbon with multiple bonds to other elements

If the carbon of the carbonyl group is attached to two other carbon atoms the compound is called a ketone,

An aldehyde contains a carbonyl group(C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen.

Oxygen double bonded to carbon is called a carbonyl group (C=O)

Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.

In an ester, the hydrogen on oxygen is replaced by a carbon atom.

acetic acid or ethanoic acid

O

O

A nitrogen attached to a carbonyl group is called an amide; the other two groups attached to nitrogen can be either both carbons, hydrogens or a mix of both carbon and hydrogen

N

A few reactions of unsaturated compounds:

Adding H2 to double bonds in vegetableoils produces compounds with higher melting points solids at room temperature, such as margarine, soft margarine, and shortening.

This makes them less reactive and less prone to become rancid; rancidness is due to reaction of the double bonds with oxygen

+H2 (catalyst)

unsaturated triglyceride saturated triglyceride

CH

CH2OCCH2CH2CH2CH2

CH2OCCH2CH2CH2CH2

CH3CH2CH2CH2CH2O

O

OCH2

CH2CH2CH2CH3

CH2

CH2

CH2

CH3CH2CH2

CH

CH2OCCH2CH2CH2CH2

CH2OCCH2CH2CH2CH2

CH3CH2CH2CH2CH2O

O

OC

CH2CH2CH2CH3

CH

C

CCH3CH2CH2

H

H

H

OH

CO

CH3CH2CH2butyric acid

C

O

C

O

Polymers are large, long-chain molecules;they are found in nature, including cellulose in plants, starches in food, and proteins and DNA in the body;they are also made synthetically, such as polyethylene and polystyrene, Teflon, and nylonthey are made up of small repeating units called monomers that are often alkenes

F

F

F

F

CH3

H

H

H CH3

CHCH2CHCH2CHCH2CHCH

CF2CF2CF2CF2CF2

CH3 CH3 CH3

Cl

H

H

H Cl

CHCH2CHCH2CHCH2CHCH

Cl Cl Cl

2

Teflon

Polypropylene

Polyvinyl chloride

Recycling is simplified by using codes found on plastic items.

Aromatic Compounds

C

CC

C

CC

H

HH

H

H

H

Different ways of representing the molecule benzene

Molecules that contain a benzene ring are often referred to as aromatic compounds, originally because of their odor

NH2 OHCH3

methylbenzene (toluene) aminobenzene (aniline) hydroxybenzene (phenol)

C

CC

C

CC HH

CH3

H

OH

H

C

CC

C

CC HH

CH2CH2CH3

H

OH

H

salicylic acid methyl salicylate

2-hydroxybenzoic acid methyl 2-hydroxybenzoate

acetosalicylic acid

C

CC

C

CC OHH

H

H

COH

O

H

C

CC

C

CC OHH

H

H

COCH3

O

H

C

CC

C

CC H

C-OH

H

H

H

O

H

benzoic acid

1-methyl,2,4,6-trimethylbenzene

C

CC

C

CC H

C

H

H

H

O H

H

benzaldehyde

4-hydroxy-3-methoxybenzaldehyde

H

H

H

HH

H

H Cl

Cl

H

HH

H

naphthalene 1,4-dichlorobenzene benzo[a]pyrene

H