Organic Chemistry

Summary 55

Summary

Organic compoundsare compounds that contain carbon.
The atomic numberof an atom equals the number of pro-
tons in its nucleus. The mass numberof an atom is the sum
of its protons and neutrons. Isotopeshave the same atomic
number, but different mass numbers.
An atomic orbitalindicates where there is a high proba-
bility of finding an electron. The closer the atomic orbital is
to the nucleus, the lower is its energy. Degenerate orbitals
have the same energy. Electrons are assigned to orbitals fol-
lowing the aufbau principle, the Pauli exclusion princi-
ple, and Hund’s rule.
The octet rulestates that an atom will give up, accept, or
share electrons in order to fill its outer shell or attain an
outer shell with eight electrons. Electropositiveelements
readily lose electrons; electronegativeelements readily ac-
quire electrons. The electronic configurationof an atom
describes the orbitals occupied by the atom’s electrons.
Electrons in inner shells are called core electrons; electrons
in the outermost shell are called valence electrons. Lone-
pair electronsare valence electrons that are not used in

bonding. Attractive forces between opposite charges are

called electrostatic attractions. An ionic bondis formed

by a transfer of electrons; a covalent bondis formed by

sharing electrons. A polar covalent bond has a dipole, mea-

sured by a dipole moment. The dipole momentof a mole-

cule depends on the magnitudes and directions of the bond

dipole moments.

Lewis structuresindicate which atoms are bonded to-

gether and show lone pairs and formal charges. A

carbocationhas a positively charged carbon, a carbanion

has a negatively charged carbon, and a radicalhas an un-

paired electron.

According to molecular orbital (MO) theory, covalent

bonds result when atomic orbitals combine to form

molecular orbitals. Atomic orbitals combine to give a

bonding MO and a higher energy antibonding MO.

Cylindrically symmetrical bonds are called sigma

bonds; pi bondsform when porbitals overlap side-to-

side. Bond strength is measured by the bond dissociation

energy. A sbond is stronger than a pbond. All single

1 P 2

1 S 2

PROBLEM 48

What is the product of each of the following reactions?

PROBLEM 49

Show how each of the following compounds reacts with

a. c. e. g.

b. +NH 4 d.BF 3 f. FeBr 3 h. CH 3 COOH

CH 3 N +CH 3 AlCl 3

+

CH 3 OH H 3

HO-:

Cl CH 3 OCH 3 CH 3

Cl CH 3

Cl

− +

Al Cl

Cl

Cl

+ Al O

aluminum trichloride

a Lewis acid

dimethyl ether

a Lewis base

HH H

H H

H

H

H

−+

BN H

H

H H

+ BN

borane

a Lewis acid

ammonia

a Lewis base

the curved arrow indicates

where the pair of electrons

starts from and where it ends up

a.ZnCl 2 + CH 3 OH c.AlCl 3 + Cl–

b. FeBr 3 + Br– d. BF 3 + HCH

O