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Overview
of alkynes
Alkynes,
or compounds containing carbon-carbon triple bonds, have properties
quite similar to that of alkenes.
In fact, many of the reactions of alkynes resemble the reactions
of alkenes. Alkynes do, however, have several properties
and reactions that are unique.
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Acetylene
is a hot-burning fuel
used in welding torches.. |
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Cicutoxin
is a toxin found in water hemlock flowers.
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Sources of alkynes |
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Orbital
description of alkenes
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Kekule
Structure
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Lewis
Structure
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Orbital
Representation
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Alkyne
carbons have two p orbitals and two sp hybridized
orbitals. The perpendicular p orbitals contain two
of the three pairs of electrons that make up the triple bond;
the last pair resides in one of the sp hybridized orbitals.
The shape of the triple bond is linear, with bonds at 180o
to each other.
Reactivity
While
very similar to alkenes in the types of reactions that they
undergo, alkynes have some unique reactions, based primarily
off the acidity of the C-H bond of acetylene (the pKa of acetylene
is 25 compared to 44 for ethylene) which can be deprotonated
by powerful bases. Alkynes are also generally more reactive
than their alkene counterparts, because of their shorter bond
length and increased electron density, shown by a comparison
of heats of formation between ethylene and acetylene (-84
kcal/mol for ethylene, -106 kcal/mol for acetylene).
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