Treatment of buta-1,3-diyne with NaNH _2 (2 equivalents), followed by reaction with excess of trans- CH _3 -CH=CH-CH _2 -Br gives X as the major product. The maximum number of carbon atoms that are collinear (in a straight line) in X is ____.
A. A
Buta-1,3-diyne (HC C - C CH) reacts with 2 equivalents of NaNH _2 to undergo double deprotonation, forming the acetylide dianion: HC C - C CH + 2 NaNH _2 \ ^ C C - C C ^ + 2 NH _3 This dianion acts as a strong nucleophile and undergoes an S_N2 reaction with the primary allylic halide, trans- CH _3 -CH=CH-CH _2 -Br (excess ensures both sides react): ^ C C - C C ^ + 2 CH _3 -CH=CH-CH _2 -Br CH _3 -CH=CH-CH _2 - C C - C C - CH _2 -CH=CH-CH _3 In the major product X , the central diyne unit consists of four sp hybridized carbon atoms. The geometry around sp hybridized carbons is linear (bond angle 180^ ). The two sp^3 hybridized - CH _2- carbons attached directly to the sp carbons also lie on this same linear axis. Thus, the sequence of collinear carbon atoms is: - CH _2 - C C - C C - CH _2- The carbon atoms beyond the - CH _2- groups are attached at a tetrahedral angle ( 109.5^ ) and are not collinear with the central axis. Therefore, the maximum number of collinear carbon atoms in X is 6. Answer: 6
Related: Chemistry — Hydrocarbons · All PYQ Banks