question_answer

A cyclic hydrocarbon molecule has all the carbon and hydrogen in a single plane. All the carbon-carbon bonds are of same length, less than \[1.54\,\overset{o}{\mathop{A}}\,\], but more than \[1.34\,\overset{o}{\mathop{A}}\,\]. The C?C bond angle will be

A)                  \[{{109}^{o}}28\]                            

B)  \[{{100}^{o}}\]

C)                  \[{{180}^{o}}\]                                

D)   \[{{120}^{o}}\]

Correct Answer: D

Solution :

                 Cyclic hydrocarbon in which all the carbon and hydrogen lies in same plane and carbon-carbon bond length between 1.34 A and 1.54 A is benzene. Due to resonance the \[C-C\]bond length is 1.39 \[\overset{o}{\mathop{A}}\,\] {ie, between 1.34 \[\overset{o}{\mathop{A}}\,\]and 1.54 \[\overset{o}{\mathop{A}}\,\]). Benzene is a hexagonal molecule and has \[s{{p}^{2}}\] hybridisation. So, the \[C-C\] bond angle will be \[{{120}^{o}}\] Note - Benzene is a resonance hybrid of two Kekute