Organic Chemistry

16 CHAPTER 1 Electronic Structure and Bonding • Acids and Bases

Kekulé Structures

In Kekulé structures, the bonding electrons are drawn as lines and the lone-pair elec-

trons are usually left out entirely, unless they are needed to draw attention to some

chemical property of the molecule. (Although lone-pair electrons may not be shown,

you should remember that neutral nitrogen, oxygen, and halogen atoms always have

them: one pair in the case of nitrogen, two pairs in the case of oxygen, and three pairs

in the case of a halogen.)

Condensed Structures

Frequently, structures are simplified by omitting some (or all) of the covalent bonds

and listing atoms bonded to a particular carbon (or nitrogen or oxygen) next to it with

a subscript to indicate the number of such atoms. These kinds of structures are called

condensed structures. Compare the preceding structures with the following ones:

You can find more examples of condensed structures and the conventions common-

ly used to create them in Table 1.5. Notice that since none of the molecules in

Table 1.5 have a formal charge or an unpaired electron, each C has four bonds, each N

has three bonds, each O has two bonds, and each H or halogen has one bond.

HCO 2 H HCN HNO 2 CH 4 CH 3 NH 2

C O H

O

H H C H C

H

H

H H C

H

H H

N H OON N H

Table 1.5 Kekulé and Condensed Structures

Kekulé structure Condensed structures

Atoms bonded to a carbon are shown to the right of the carbon. Atoms other than H can be shown hanging from the carbon.

Repeating groups can be shown in parentheses.

Groups bonded to a carbon can be shown (in parentheses) to the right of the carbon, or hanging from the carbon.

Groups bonded to the far-right carbon are not put in parentheses.

HHC

H

HH H OH

C

H

C

CH 3

CH 3

CCH 3 CH 2 C(CH 3 ) 2 CH 2 CH 2 OH or CH 3 CH 2 CCH 2 CH 2 OH

H

CH 3

CH 3

C

H

HHC

H

HH H OHH

C

H

C

H

CH 3

CCH 3 CH 2 CH(CH 3 )CH 2 CH(OH)CH 3 or CH 3 CH 2 CHCH 2 CHCH 3

H

CH 3 OH

C

H H

C

HHC

H

H

C

H

C

H

CCH 3 CH 2 CH 2 CH 2 CH 2 CH 3 or CH 3 (CH 2 ) 4 CH 3

H

H

C

H

C

H

HHH H

CH 2

HHC

H

H

C

H

Br

C

H

H

CCH 3 CHBrCH 2 CH 2 CHClCH 3 or CH 3 CHCH 2 CH 2 CHCH 3

H

H

C

H

Cl Br Cl

C

H

H