Page 23 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

2 Scheme 1.1. Lewis Structures of Simple Molecules

CHAPTER 1 Single Bonds
Chemical Bonding
and Molecular Structure H H H H H H H H
H C H H C O H H C C H H C C O H H C . . C H
. . O
H H H H H H H H
methane methanol ethane ethanol dimethyl ether

Double Bonds
H H H H H H
H H C H H C C
C C H C C C O H C C O H C C O
H H H H H H OH
ethene propene methanal ethanal ethanoic acid
(ethylene) (propylene) (formaldehyde) (acetaldehyde) (acetic acid)

Triple Bonds H
H H
– +
H C C H H C C C C H C O H C C N
H H H
ethyne
(acetylene) 2-butyne carbon monoxide ethanecarbonitrile
(acetonitrile)

how structure effects the energy of transition structures and intermediates in chemical
reactions. The principal goal of this chapter is to discuss the concepts that chemists use
to develop relationships between molecular structure and reactivity. These relationships
have their foundation in the fundamental physical aspects of molecular structure, that
is, nuclear position and electron density distribution. Structural concepts help us see,
understand, and apply these relationships.

1.1. Description of Molecular Structure Using Valence Bond Concepts

Introductory courses in organic chemistry usually rely primarily on the valence
bond description of molecular structure. Valence bond theory was the first structural
theory applied to the empirical information about organic chemistry. During the second
half of the nineteenth century, correct structural formulas were deduced for a wide
variety of organic compounds. The concept of “valence” was recognized. That is,
carbon almost always formed four bonds, nitrogen three, oxygen two, and the halogens
one. From this information, chemists developed structural formulas such as those in
Scheme 1.1. Kekule’s structure for benzene, published in 1865, was a highlight of
this period. The concept of functional groups was also developed. It was recognized
that structural entities such as hydroxy (−OH), amino (–NH , carbonyl (C=O), and
2