The major product of the following reaction is:

This is a Friedel-Crafts alkylation of benzene. The alkylating electrophile is generated by protonating the provided alkene using a strong acid catalyst.

Step 1: Protonation and Carbocation Formation

The sulfuric acid provides a proton $$\mathrm{(H^+)}$$ that attacks the electron-rich double bond of the alkene. Following Markovnikov’s rule, the proton adds to the terminal $$\mathrm{CH_2}$$ carbon to generate a secondary carbocation.

$$\mathrm{CH_3-CH(NO_2)-CH=CH_2 + H^+ \longrightarrow CH_3-CH(NO_2)-C^+H-CH_3}$$

While the adjacent nitro group $$\mathrm{(-NO_2)}$$ destabilises this intermediate through its strong electron-withdrawing inductive effect $$\mathrm{(-I)}$$, the secondary carbocation is still more stable than the alternative primary carbocation.

Step 2: Checking for Rearrangements

Carbocations often undergo hydride or alkyl shifts to form a more stable carbocation. Consider a possible hydride shift:

$$\mathrm{CH_3-CH(NO_2)-C^+H-CH_3 \xrightarrow{\text{Potential Hydride Shift}} CH_3-C^+(NO_2)-CH_2-CH_3}$$

If this shift occurred, the positive charge would be placed adjacent to the nitrogen atom of the nitro group. Since nitrogen in the $$\mathrm{-NO_2}$$ group already carries a formal positive charge, placing another positive charge nearby is highly unstable.

Therefore, no rearrangement occurs.

Step 3: Electrophilic Aromatic Substitution (EAS)

The benzene ring acts as a nucleophile and attacks the secondary carbocation. Aromaticity is restored after loss of a proton.

$$\mathrm{C_6H_6 + CH_3-CH(NO_2)-C^+H-CH_3 \longrightarrow C_6H_5-CH(CH_3)-CH(NO_2)-CH_3 + H^+}$$

The Major Product:

The final major product is $$\mathrm{(3\text{-}nitrobutan\text{-}2\text{-}yl)benzene}$$ or $$\mathrm{2\text{-}phenyl\text{-}3\text{-}nitrobutane}$$.

Structure:

$$\mathrm{Ph-CH(CH_3)-CH(NO_2)-CH_3}$$