Untitled - Kelly Walsh High School

318 CHEMISTRY FOR THE UTTERLY CONFUSED
Quick Tip
The following illustrates the hydrogenation and halogenation, with bromine, of
the alkene propene. Notice that the [CH 3 group, which is not a functional
group, does not change during either reaction.
CH 2 CH CH 3 +
CH 2 CH CH 3 +
The hydrogenation of an alkyne can give two possible products. If there is a limited
quantity of hydrogen available, hydrogenation converts an alkyne to an
alkene. If more hydrogen is available, the alkene will react to become an
alkane. The following illustrates the hydrogenation of propyne. Only the first
step occurs if there is not much hydrogen, while the second step occurs if there
is sufficient hydrogen remaining after the first step.
CH C CH3 +
H H
CH C CH 3
+
H 2
Cl 2
H 2
H 2
catalyst
Catalyst
Catalyst
Cl Cl
H H
CH 2 CH CH 3
CH 2 CH CH 3
H H
CH C CH 3
H H
CH C CH 3
H H
If you are told to use 2 mol of hydrogen or excess hydrogen, the second result
is the answer.
The halogenation of an alkyne, like hydrogenation, can give two possible products.
A limited amount of halogen will only add one molecule, whereas an
excess of halogen will add two molecules.
The other functional groups participate in a variety of reactions. We have
already seen some of these reactions. The carboxylic acids will behave as typical
weak acids. The amines will behave as typical weak bases. The only other
category of reaction we will examine here is a condensation reaction.