The table shows the typical bond length of carbon–carbon bonds. Which of the following values seems most reasonable for the carbon–carbon bonds’
length in benzene? (A) 110 picometers, (B) 120 picometers, (C) 130 picometers, (D) 140 picometers, or
(E) 160 picometers.
Benzene is a cyclic hydrocarbon that contains six carbon atoms and six hydrogen
atoms. It is also known as an aromatic hydrocarbon. There have been many forms of experimental analyses performed to understand the
structure of benzene, including by Kathleen Lonsdale who did very important work on
understanding carbon–carbon bond lengths.
In her work, using X-ray diffraction analysis, she demonstrated that all
carbon–carbon bond lengths in benzene were the same. She showed that the distance between adjacent benzene carbon atoms is less than the
distance between a typical carbon–carbon single bond, which is usually about 154
picometers. She observed that it was also longer than a typical carbon–carbon double bond of 134
picometers. It is because we know that benzene carbon–carbon bonds exhibit characteristics
somewhere between a single bond and a double bond that we can assume that the length
should be between that of a single bond and a double bond.
And with that understanding, we should be able to revisit and answer the
question. The table below shows the typical bond length of carbon–carbon bonds. Which of the following values seems most reasonable for the carbon–carbon bonds’
length in benzene? And since there is only value that lies between 134 and 154 picometers, we can
correctly choose answer choice (D), 140 picometers.