Which two organic chemists are known for observing the peroxide effect in adding reagents to unsaturated compounds in 1933?

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1. Historical fact: The "peroxide effect" (also called the Kharasch effect) — the peroxide-initiated anti-Markovnikov addition of HBr to alkenes — was first reported by Morris S. Kharasch and Frank R. Mayo in 1933.

2. Observation: In the presence of peroxides (ROOR) the addition of HBr to an alkene gives the anti-Markovnikov product. Example: $\mathrm{CH_3CH=CH_2 + HBr \xrightarrow{ROOR} CH_3CH_2CH_2Br}$.

3. Mechanism (brief): Peroxides decompose to radicals, initiating a radical chain in which bromine radicals add to the alkene and lead to the reversed regiochemistry compared with the ionic (Markovnikov) pathway.

4. Conclusion: The pair credited with this 1933 observation is Morris S. Kharasch and Frank R. Mayo, so option (1) is correct.

FINAL_ANSWER: a

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