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Alkenes Notes

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Unit 2: 15 Alkenes

ALKENES

-Alkenes are unsaturated (contain a C=C double bond)
-General formula CnH2n
-Functional group - double bond

SHAPES OF ALKENES This arrangement is planar, because the carbon atoms in the C=C bond and the atoms bonded to these carbs all lie in the same plane.
-The shape is trigonal planar about each unsaturated carbon, with the bond angle 120°.

The H atoms on the methyl groups, CH3 are non-planar (not in the same plane as the double bond unit) - the methyl groups have CH3 tetrahedral shape. E-Z STEREOISOMERISM - restricted rotation about the C=C bond means that alkenes can exhibit E-Z stereoisomerism (also known as geometric isomerism or cis-trans isomerism) STEREOISOMERISM - compounds with the same structural formula but with atoms arranged differently in space. CRITERIA - a C=C bond must be present

- each carbon in the double bond must have 2 different groups attached.

(Z) steroisomerism - higher Ar groups on the same side of the double bond (E) stereoisomerism -higher Ar groups on opposite sides of the double bond

(Z)

(Z)

CHEMISTRY AS NOTES

(E)

(E)

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