Organic Chemistry

80 CHAPTER 2 An Introduction to Organic Compounds

2.8 Structures of Alkyl Halides, Alcohols, Ethers,

and Amines

The bond (where X denotes a halogen) of an alkyl halide is formed from the

overlap of an orbital of carbon with an orbital of the halogen (Section 1.13).

Fluorine uses a orbital, chlorine a orbital, bromine a orbital, and

iodine a orbital. Because the electron density of the orbital decreases with increas-

ing volume, the bond becomes longer and weaker as the size of the halogen in-

creases (Table 2.4). Notice that this is the same trend shown by the bond

(Table 1.6, page 36).

The oxygen of an alcohol has the same geometry it has in water (Section 1.11). In

fact, an alcohol molecule can be thought of as a water molecule with an alkyl group in

place of one of the hydrogens. The oxygen atom in an alcohol is hybridized, as it is

in water. One of the orbitals of oxygen overlaps an orbital of a carbon, one

orbital overlaps the sorbital of a hydrogen, and the other two orbitals each contain

a lone pair.

The oxygen of an ether also has the same geometry it has in water. An ether molecule

can be thought of as a water molecule with alkyl groups in place of both hydrogens.

O

an alcohol electrostatic potential

map for methanol

H

R

sp^3 hybridized

sp^3

sp^3 sp^3 sp^3

sp^3

H¬X

C¬X

5 sp^3

2 sp^33 sp^34 sp^3

sp^3 sp^3

C¬X

Carbon–Halogen Bond Lengths and Bond Strengths

Bond

lengths

Orbital Bond strength

interactions kcal/mol kJ/mol

H 3 F 108 451

H 3 Cl 84 350

H 3 Br 70 294

H 3 I 57 239

I

H

H

H

C

C

C

C

2.14 A

I

Br

H

H

H

1.93 A

Br

Cl

H

H

H

1.78 A

Cl

H

H

H F

1.39 A

F

C

C

C

C

C

C

C

C

Table 2.4

Tutorial:

Functional groups

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