Carbon- carbon double bonds do not freely rotate like carbon- carbon single bond

Question

Carbon- carbon double bonds do not freely rotate like carbon- carbon single bond. Why? A) The double bond is much stronger and thus more difficult to rotate. B) Overlap of the two 2p orbital of the pi bond would be lost. C) The shorter bond length of the double bond makes it more difficult for the attached group to pass each other. D) Overlap of the sp^2 orbital of the carbon- carbon sigma bond would be lost. The major product (s) of this reaction would be A) only (R) B) only (S) C) (R) and (S) D) achiral When a strong base is used in the elimination reaction of an alky 1 halide the mechanism, in general, is A) E1. B) E2. C) E1 for tertiary halides, E2 for primary and secondary halides. D) E2 for tertiary halides, EI for primary and secondary halides. Arrange the following carbocations in order of their decreasing stabilities (most stable first). A) I > II > III B) III > II > I C) I > III > II D) II > III > I

Explanation / Answer

Q15.

Note that

a single bond is done by a single sigma bond. This is essentially overlaping two sp3 orbitals.

For a double bond, note that sp2 must form a sigma + pi bond

the pi bond is vertical and will not allow roation

so

a) this is false, even though this is stronger, it is NOT the reason

b) False,

c) This is correct, the pi bond will not allow rotation

d) false, sigma bodn is not lost

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