Alkenes: Structure and Preparation via Elimination Reactions PDF
Preview Alkenes: Structure and Preparation via Elimination Reactions
Naming double bond-containing substituents IUPAC: alkenyl 1-(2-butenyl)-2-methyl-1-cyclohexene Naming double bond-containing substituents IUPAC: alkenyl 1-(2-butenyl)-2-methyl-1-cyclohexene Some common double bond-containing substituents: vinyl (ethenyl) 1-methyl-4-vinyl-1-cyclohexene Naming double bond-containing substituents IUPAC: alkenyl 1-(2-butenyl)-2-methyl-1-cyclohexene Some common double bond-containing substituents: vinyl (ethenyl) 1-methyl-4-vinyl-1-cyclohexene allyl (2-propenyl) 1-allyl-4-vinyl-1-cyclohexene Naming double bond-containing substituents IUPAC: alkenyl 1-(2-butenyl)-2-methyl-1-cyclohexene Some common double bond-containing substituents: vinyl (ethenyl) 1-methyl-4-vinyl-1-cyclohexene allyl (2-propenyl) 1-allyl-4-vinyl-1-cyclohexene phenyl 4,4-dimethyl-1-phenyl-1-cycloheptene Naming double bond-containing substituents IUPAC: alkenyl 1-(2-butenyl)-2-methyl-1-cyclohexene Some common double bond-containing substituents: vinyl (ethenyl) 1-methyl-4-vinyl-1-cyclohexene allyl (2-propenyl) 1-allyl-4-vinyl-1-cyclohexene phenyl 4,4-dimethyl-1-phenyl-1-cycloheptene benzyl (phenylmethyl) (R)-1-benzyl-4-methyl-4-phenyl-1-cycloheptene When the parent chain contains multiple C=C, use a multiplicative prefix before “ene”: Cl (S)-6-chloro-4-methyl-2,4-heptadiene Alenes are classified according to their degree of substitution of the C=C functional group H monosubstituted H H H disubstituted H H terminally disubstituted H trisubstituted H tetrasubstituted How strong is a C=C ? Is it twice the strength of a C–C? B F F H1s H1s F Csp2 Csp2 H1s F H1s F ∆H , kcal/mol DBE . . H C CH CH + CH 83 1 σ 3 3 3 3 146 1 σ + 1 π H C CH :CH + :CH 2 2 2 2 ˆ ∆H (1 σ + 1 π) - ∆H (1 σ ) = ∆H (1 π) BDE BDE BDE 146 - 83 = 63 cis-alkenes and trans-alkenes Consider all the isomers of the alkene C H : 4 8 are these conformational isomers? • No! They are isomers that differ by the relative positions of the substituent methyl groups in space. • They cannot be converted into each other without breaking a bond. • Therefore, they are diastereoisomers. • Why does rotation about the C=C break a bond? H H H H C C C CH CH CH H3C C 3 C 3 H C 3 H H C CH 3 3 π π π bond no bond bond reforms These diastereoisomers are named just like disubstituted cycloalkanes: E • Identical groups on the same side of the C=C (that is, with a 0 dihedral angle) are cis-alkenes E • Identical groups on opposite sides of the C=C (that is, with a 180 dihedral angle) are trans-alkenes
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