Compound A (C7H11Br) is treated with magnesium in ether to give B (C7H11MgBr), which reacts violently with D2O togive 1-methylcyclohexene with a deuterium atom on the methyl group (C). Reaction of B with acetone (CH3COCH3)followed by hydrolysis gives D (C10H18O). Heating D with concentrated H2SO4 gives E (C10H16), which decolorizestwo equivalents of Br2 to give F (C10H16Br4). E undergoes hydrogenation with excess H2 and a Pt catalyst to giveisobutylcyclohexane. Determine the structures of compounds A through F, and show your reasoning throughout
The Correct Answer and Explanation is:
To solve this problem, let’s break down each step of the reaction and determine the structure of each compound based on the provided information.
Compound A (C7H11Br):
- Structure: Compound A is likely a bromoalkane. Given that it’s treated with magnesium to form a Grignard reagent, it suggests that A is a bromocyclohexane derivative.
- Reasoning: The presence of a bromine atom indicates that A is likely 1-bromocyclohexane (C7H11Br), where the bromine is attached to the cyclohexane ring.
Compound B (C7H11MgBr):
- Structure: Compound B is the Grignard reagent, formed by reacting compound A with magnesium in ether. This results in the formation of a cyclohexylmagnesium bromide (C7H11MgBr).
- Reasoning: The magnesium inserts between the carbon-bromine bond, forming the Grignard reagent, where the bromine is replaced by a magnesium-bromine bond.
Reaction with D2O:
- When compound B reacts with D2O (heavy water), the result is 1-methylcyclohexene with a deuterium atom on the methyl group (C).
- Structure of C: The reaction forms 1-methylcyclohexene (C7H12) with a deuterium atom replacing the hydrogen on the methyl group. This suggests the formation of a deuterated 1-methylcyclohexene.
- Reasoning: The Grignard reagent acts as a strong base and abstracts a proton from D2O, replacing it with a deuterium atom (D).
Compound D (C10H18O):
- Structure: Reaction of B with acetone (CH3COCH3) forms an addition product. The Grignard reagent adds to the carbonyl group of acetone, resulting in a tert-butyl alcohol structure after hydrolysis.
- Reasoning: The product is D, a tertiary alcohol with the formula C10H18O, which matches the structure of 2-methyl-2-pentanol (a product of the Grignard reaction with acetone).
Compound E (C10H16):
- Structure: Heating compound D with concentrated H2SO4 leads to dehydration, resulting in the formation of E, a cyclohexene derivative (C10H16).
- Reasoning: The dehydration removes water from the alcohol, forming a double bond to create a cyclohexene structure, specifically 1-methylcyclohexene.
Compound F (C10H16Br4):
- Structure: Decolorization of bromine in the presence of compound E indicates the presence of a reactive alkene. The alkene reacts with two equivalents of Br2, leading to the formation of a tetra-bromo derivative.
- Reasoning: The dibromination occurs across the double bond of 1-methylcyclohexene, resulting in F, which is 1,2,3,4-tetrabromocyclohexane (C10H16Br4).
Final Structure of Compounds A–F:
- A (C7H11Br): 1-bromocyclohexane.
- B (C7H11MgBr): Cyclohexylmagnesium bromide.
- C (C7H12D): 1-deuterated methylcyclohexene.
- D (C10H18O): 2-methyl-2-pentanol (tert-butyl alcohol).
- E (C10H16): 1-methylcyclohexene.
- F (C10H16Br4): 1,2,3,4-tetrabromocyclohexane.
This sequence describes the formation and transformations of each compound, leading to their final structures.
