1

Chapter 4Carbon and the

Molecular Diversity of Life

2

Carbon Chemistry• Carbon is the backbone of biological

molecules (macromolecules)• All living organisms are made up of

chemicals based mostly on the element carbon

Figure 4.1

3

Carbon Chemistry• Organic chemistry is the study of

carbon compounds• Carbon atoms can form diverse molecules

by bonding to four other atoms• Carbon compounds range from simple

molecules to complex ones• Carbon has four valence electrons and

may form single, double, or triple.

4

• The bonding versatility of carbon allows it to form many diverse molecules, including carbon skeletons

(a) Methane

(b) Ethane

(c) Ethene (ethylene)

Molecular Formula

Structural Formula

Ball-and-Stick Model

Space-Filling Model

HH

HH

HH

H

HH

H

H HHH

C

C C

C C

CH4

C2H6

C2H4

Name and Comments

Figure 4.3 A-C

5

• The electron configuration of carbon gives it covalent compatibility with many different elements

H O N C

Hydrogen(bonds = 1)

Oxygen(bonds = 2)

Nitrogen(bonds = 3)

Carbon(bonds = 4)

Figure 4.4

6

• Carbon may bond to itself forming carbon chains

• Carbon chains form the skeletons of most organic molecules

• Carbon chains vary in length and shape

HHH

HH

H H H

HH

H

H H H

H H HH H

H

H

H

H

H

H

HH

HH H H H

H HH H

H H H H

H H

H HHHHH H

HH

C C C C C

C C C C C C C

CCCCCCCC

C

CC

CC

C

CCC

CCC

H

H

H

HHH

H

(a) Length

(b) Branching

(c) Double bonds

(d) Rings

Ethane Propane

n-Butane isobutane

1-Butene 2-Butene

Cyclohexane Benzene

H H H HH

Figure 4.5 A-D

7

Hydrocarbons• Hydrocarbons are molecules consisting of

only carbon and hydrogen• Hydrocarbons Are found in many of a cell’s organic

molecules

(a) A fat molecule (b) Mammalian adipose cells100 µm

Fat droplets (stained red)

Figure 4.6 A, B

8

Isomers• Isomers are molecules with the same

molecular formula but different structures and properties

• Three types of isomers are– Structural– Geometric– Enantiomers

H H H H HH

H H H H HH

HHH

HH

H

H

H

H

HHH

H

H

H

H

CO2H

CH3

NH2C

CO2H

HCH3

NH2

X XX

X

C C C C C

CC

C C C

C C C C

C

(a) Structural isomers

(b) Geometric isomers

(c) Enantiomers

H

Figure 4.7 A-C

9

• Enantiomers Are important in the pharmaceutical industry

L-Dopa(effective against Parkinson’s disease)

D-Dopa(biologically inactive)Figure 4.8

10

Functional Groups• Functional groups

are the parts of molecules involved in chemical reactions

• They are the chemically reactive groups of atoms within an organic molecule

• They give organic molecules distinctive chemical properties

CH3OH

HO

O

CH3

CH3OH

Estradiol

Testosterone

Female lion

Male lionFigure 4.9

11

• Seven functional groups are important in the chemistry of life– Hydroxyl– Carboxyl– Amino– Phosphate– Carbonyl– Methyl– Sulfhydryl

12

Some important functional groups of organic compounds

FUNCTIONALGROUP

STRUCTURE

(may be written HO )

HYDROXYL CARBONYL CARBOXYL

OH

In a hydroxyl group (—OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (Do not confuse this functional group with the hydroxide ion, OH–.)

When an oxygen atom is double-bonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (—COOH).

CO O

COH

Figure 4.10

The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond.

13

Some important functional groups of organic compounds

Acetic acid, which gives vinegar its sour tatste

NAME OF COMPOUNDS

Alcohols (their specific names usually end in -ol)

Ketones if the carbonyl group is within a carbon skeleton Aldehydes if the carbonyl group is at the end of the carbon skeleton

Carboxylic acids, or organic acids

EXAMPLE

Propanal, an aldehyde

Acetone, the simplest ketone

Ethanol, the alcohol present in alcoholic beverages

HH

H

H H

C C OHH

H

H

HH

H

HC C H

C

C C

C C C

O

H OH

O

H

HH H

H O

HFigure 4.10