Q.Which of the following compounds shall not produce propene by reaction with HBr followed by elimination (or) only direct elimination reaction (NEET)

Step 1. Cyclopropane + HBr opens the strained three-membered ring (an addition reaction driven by ring strain) to give 1-bromopropane, which then eliminates HBr (with a strong base) back to propene -- this route works.

Step 2. n-Propanol (CH3CH2CH2OH) + HBr gives 1-bromopropane directly (substitution), which eliminates to propene; alternatively, propanol can be directly acid-dehydrated (E1) straight to propene without ever forming the bromide -- either way, this route works.

Step 3. n-Propyl bromide (CH3CH2CH2Br) needs no HBr addition step at all -- it already IS the alkyl bromide, and direct elimination (alcoholic KOH) converts it straight to propene -- this route works. …

For each option, check first whether its carbon count can even reach propene's three carbons, then check whether an HBr-addition/eliminat …

• Overlooking the simplest disqualifying fact first (ketene has only 2 carbons, so it can never give a 3-carbon product) and instead trying to reason through unfamiliar addition chemistry on the C=C=O system. …