Structure and Reactivity of 2-Methylbut-1-ene

Steps:

• The structure is CH₂=C(CH₃)CH₂CH₃, with the double bond between carbons 1 (CH₂) and 2 (C(CH₃)CH₂CH₃).
• For geometrical isomers, each double-bond carbon needs two different substituents; carbon 1 has two H atoms, preventing cis-trans isomerism.
• HBr addition follows Markovnikov's rule: H adds to carbon 1 (less substituted), forming a tertiary carbocation at carbon 2, so Br adds there, yielding 2-bromo-2-methylbutane (CH₃CBr(CH₃)CH₂CH₃).
• Student 1 is wrong (no geometrical isomers); Student 2 is wrong (main product is 2-bromo-2-methylbutane, not 1-bromo-2-methylbutane).

Why D is correct:

• Neither statement holds: no geometrical isomers due to identical substituents on one alkene carbon, and HBr product follows Markovnikov's rule for the tertiary halide.

Why the others are wrong:

• A: Both students incorrect, as structure lacks geometrical isomerism and addition gives the wrong major product.
• B: Student 1 wrong; terminal =CH₂ prevents geometrical isomers.
• C: Student 2 wrong; Markovnikov addition places Br at the tertiary carbon, not primary.

Final answer: D