Chapter 12 Alkenes, Alkynes, and Aromatic Compounds Compounds with multiple bonds The most ...

23 Pages·2012·0.78 MB·English

Chapter 12 Alkenes, Alkynes, and Aromatic Compounds
Compounds with multiple bonds
The most important compound with a triple bond
is ethyne also known as acetylene;
it is used in the oxy acetylene torch.
Bombykol, is another natural product that contains
double bonds. We will examine the structure of
these materials shortly
Compounds of carbon and hydrogen with less tha 2n+ 2 hydrogens other than cyclic
hydrocarbons
Is there any other way of satisfying the octet for carbon in a molecule with a formula
C H or C H ?
2 4 2 2
How many groups around each C? 3
(bonding electrons are not considered
to be a group)
H H
::
C C
H H
What’s the geometry? triangular
How about C H ?
2 2
How many groups around each C? 2
≡
H C C H
What’s the geometry? linear
ethene or ethylene
What does ethylene have to do with fruit?
A systematic way of naming alkenes and identifying identical structures
1. Locate the longest carbon chain in the molecule that contains the double bonds: this
identifies the parent alkene
2. Identify the points of branching and count the number of carbons in each branch; name
the alkyl branches in the normal way: methyl, ethyl ...
3. Give the double bond the lowest number
4. Identify any stereochemistry
parent: 4 carbons: butene
CH CH groups: 2 carbons: ethyl
2 3
H C C location:
2 double bond at position 1; ethyl at 2
CH
2
CH
3
2-ethyl-1-butene no stereochemistry to describe
Are these two compounds the same?
All these formulas for butane are identical
because of rapid rotation about C-C bonds
If the two groups are on the same
side of the double bond, use cis
On opposite sides, use trans
no, rotation about C=C bonds does not occur
CH -CH
2 3
CH parent: cyclohexane
H C CH
2 2 groups: ethyl, chloro
location: 1, 3
H C CH
2
CH Cl
2
CH CH
2 3
CH CH
2 3
Cl
Cl
The solid wedge is used to denote a group sticking out of the plane of the screen
A dotted wedge is used to denote a group sticking out of the plane of the screen
Two groups with the same relative orientation is called cis
Two groups with the opposite relative orientation is called trans
Naming compounds with double and triple bonds
ethane
H C CH
generic names alkane 3 3
ethene or ethylene
alkene
H C CH
2 2
alkyne
ethyne or acetylene
H C C H
H
H
C C
CH CH H CH CH
3 3 cis 2-butene 2 3
H
H
H H
1-butene
H CH CH
CH H 2 3
3 trans 2-butene
H CH
3
1-butyne
H C C CH CH
2 3
2-butyne
CH C C CH
3 3
H
CH CH CH CH
2 2 2 3
Name the following: C C
CH CH CH H
3 2
CH
3
parent: nonene
groups: methyl, double bond
location:
3-methyl, 4-double bond
stereochemistry: trans
trans 3-methyl-4-nonene
H CH
3
C
parent: cyclohexene
H C CH
2
groups: methyl
H C CH
2
CH location:
2 1, 3 or 1,2?
shorthand notation
3-methyl-1-cyclohexene or
1-methyl-2-cyclohexene
A pheromone is a chemical messenger emitted
by insects in minute quantities.
Bombykol is emitted by the silkworm moth to
attract other moths and has one cis and one
trans double bond
16 C: hexadecane parent alkane
2 double bonds diene
alcohol: drop the last e and add ol
stereochemistry: cis and trans
(CH ) means 7 CH groups in a row
2 7 2
To name this compound we need to know how to name a compound with 16 carbon atoms
How to name compounds with more than one double bond
How to name alcohols and how to designate “stereochemistry” (the arrangement of groups in
space:
trans10, cis 12-hexadecadien-1-ol
Name the following:
Br Br parent: ethene cis-1,2-Dibromoethene
groups: bromo
A. C C
location 1,2
stereochemistry cis
H H
:
CH H
3
parent: butene
C C trans-2-Butene
B.
groups: double bond
H CH location: 2

3
stereochemistry: trans
CH Cl
3
parent: propene
C.
C C groups: chloro
1,1-Dichloropropene
location: 1,1
H Cl
stereochemistry: none