Which of the following nucleophiles adds preferentially in a 1,2-manner (as oppo

Question

Which of the following nucleophiles adds preferentially in a 1,2-manner (as opposed to 1,4- addition) to unsaturated ketones? k. Ph2CuLi . SH m. PhMgBr n. PhCOCH2 o. PPh What is the major product when acrolein (H2C-CH -CHO) is treated with lithium diethylcuprate (Et CuLi)? OH Et Et Et 12 13 Et 15 q. 12 r. 13 s. 14 t. 15 The compound below was prepared using an aldol reaction between diacetyl (CH3COCOCH3) and acetaldehyde (CH:CHo). Which of the following statements about this reaction is true? CH3 CH3 u. Acetaldehyde serves as the nucleophile in this reaction. v. The reaction gives an unequal mixture of enantiomers. w. Alkoxide base can be used to promote this reaction. x. Aldol condensatio n of the product shown would g unsaturated aldehyde. Diacetyl serves as the nucleophile in this reaction. y.

Explanation / Answer

Ans 1. m . PhMgBr

The grignard reagents such as Phenyl magnesium Bromide are strong nucleophiles , which add 1,2 and 1,4 to the unsaturated ketones irreversibily but since 1,2 additions to the carbonyl groups are faster , there is a predominance of 1,2 products in these reactions .

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