The maximum number of RBr producing 2-Methylbutane by above sequence of reactions is __________. (Consider the…

Step 1: Understand the reaction sequence

The reaction is a Grignard reaction followed by hydrolysis:

1. $\ce{RBr + Mg ->[dry ether] RMgBr}$ (Grignard reagent)
2. $\ce{RMgBr + H2O -> R-H + Mg(OH)Br}$ (protonation)

Net result: $\ce{RBr -> R-H}$ (replacement of Br with H)

Step 2: Identify the target structure

2-Methylbutane: $\ce{CH3-CH(CH3)-CH2-CH3}$

Structure:

      CH3
       |
CH3-CH-CH2-CH3

Molecular formula: $\ce{C5H12}$

Step 3: Determine possible RBr isomers

To get 2-methylbutane ($\ce{C5H12}$), we need $\ce{C5H11Br}$ isomers that, upon replacing Br with H, give 2-methylbutane.

Possible positions for Br in the 2-methylbutane skeleton:

1. C-1 (terminal): $\ce{BrCH2-CH(CH3)-CH2-CH3}$ → 1-bromo-2-methylbutane
2. C-2 (branched): $\ce{CH3-CBr(CH3)-CH2-CH3}$ → 2-bromo-2-methylbutane
3. C-3: $\ce{CH3-CH(CH3)-CHBr-CH3}$ → 3-bromo-2-methylbutane
4. C-4 (terminal): $\ce{CH3-CH(CH3)-CH2-CH2Br}$ → 4-bromo-2-methylbutane

Wait, position 4 is the same as position 1 by symmetry? Let me check:

• C-1: $\ce{BrCH2-CH(CH3)-CH2-CH3}$
• C-4: $\ce{CH3-CH(CH3)-CH2-CH2Br}$

These are different! C-1 is on the branch side, C-4 is on the longer chain side.

Actually, let me number correctly:

        4  3  2  1
           CH3
            |
    CH3-CH2-CH-CH3

No wait, 2-methylbutane numbering:

    1    2   3   4
   CH3-CH-CH2-CH3
        |
       CH3 (branch)

Positions for Br:

1. C-1: $\ce{BrCH2-CH(CH3)-CH2-CH3}$
2. C-2: $\ce{CH3-CBr(CH3)-CH2-CH3}$
3. C-3: $\ce{CH3-CH(CH3)-CHBr-CH3}$
4. C-4: $\ce{CH3-CH(CH3)-CH2-CH2Br}$

But C-4 and C-1 are NOT the same because the methyl branch is at C-2.

Actually, all 4 positions give different bromides.

Answer: (a) 4

Key Points:

• Grignard + H₂O → replaces halogen with hydrogen
• Count all unique positions where Br can be placed
• Consider structural isomers only (not stereoisomers)