Chemistry - Hydrocarbon Question with Solution | TestHub
Given below are two statements:
Statement I:
trans-But-2-ene upon treatment with Br in CCl gives the following product
Statement II:
cis-But-2-ene upon treatment with alkaline KMnO gives the following product
In the light of the above statements, choose themost appropriateanswer from the options given below.NEET 2026 (Re-NEET)
Options:
Answer:
Solution:
Reaction of trans-but-2-ene with Br in CCl proceeds via anti-addition to give meso-2,3-dibromobutane.
In the Newman projection given in Statement I, the front carbon has Br at , Me at , and H at . The back carbon has Br at , Me at , and H at . For this staggered conformation to be meso, it must have a center of inversion, meaning a group at angle on the front carbon must have an identical group at on the back carbon. While the Br atoms are opposite ( and ), the front Me at is not opposite to the back Me at . Thus, it lacks a center of inversion and represents a chiral enantiomer. Hence, Statement I is incorrect.
Reaction of cis-but-2-ene with alkaline KMnO proceeds via syn-addition to give meso-butane-2,3-diol.
In the Newman projection given in Statement II, the front carbon has OH at , Me at , and H at . The back carbon has OH at , Me at , and H at . Rotating the back carbon by counter-clockwise perfectly eclipses all identical groups (OH with OH at , Me with Me at , H with H at ). This indicates the presence of a plane of symmetry, confirming it is the meso isomer. Hence, Statement II is correct.
Therefore, Statement I is incorrect but Statement II is correct.
Answer:Statement Iis incorrect butStatement IIis correct
