Which alkyl halide should be used to prepare
pent-2-ene and why?
To prepare pent-2-ene, we need to start with an alkyl halide that can undergo an elimination reaction called dehydrohalogenation. In this reaction, a hydrogen halide (such as HBr or HI) is removed from the alkyl halide, resulting in the formation of a double bond.
In this case, we want to prepare pent-2-ene, which is a 5-carbon compound with a double bond located on the second carbon atom. To achieve this, we need an alkyl halide that has a halogen atom attached to the second carbon atom.
Among the possible alkyl halides, one option is 2-bromopentane (CH3CHBrCH2CH2CH3). This alkyl halide has a bromine atom attached to the second carbon, as desired.
The dehydrohalogenation of 2-bromopentane can be carried out by treating it with a strong base, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH), in an alcoholic solvent like ethanol or methanol. The strong base will abstract a hydrogen ion (H+) from the carbon adjacent to the bromine atom, leading to the removal of HBr and formation of the double bond on the second carbon atom.
Thus, 2-bromopentane is the appropriate alkyl halide to use for the preparation of pent-2-ene in this case.