Question

When carbene attacks cis 2-butene singlet gives cis product while triplet gives trans product. Why ?
answer required

Answer 1

Addition of carbene to an alkene is usually formulated in terms of attack of its vacant orbitals since a singlet carbene adds to an elefin in a stereospecific manner while the triplet does not. Thus addition of singlet :CH2 to cis-l, 2- disubstituted alkene gives cis-l, and triplet carbene to trans-l, 2-disubstituted alkene affords the corresponding trans- product.