Alkene - Properties, Nomenclature, Reaction, Isomers, Synthesis

Properties: Similar to alkane; non-polar, flammable




C=C; cumulative -C=C=C-


• Polyunsaturated fatty acid: 2 or more C=C


• Allene: adjacent C=C=C


• Vinyl group: H2C=CH-


• Methylene group: H2C=


• Allyl group: H2C=CH-CH2-


• Vinyl halide: halide replaces -H on >C=C<


• Conjugated: alternate C-C and C=C (resonance)


• Alkadiene, 2 conjugated C=C; example: butadiene;

s-cis and s-trans (rotate about C-C bond)


• Alkatriene, 3 conjugated C=C


• Annulene: conjugated monocyclic compound;

example: [6] annulene = benzene


• Aromatic cyclic ions: cyclopentadiene anion,

cycloheptatriene cation (6 electrons)


• Add -ene to prefix; Use # to denote C=C position


• Isolated C-C=C-C-



no free rotation of C=C


• E/Z; prioritize groups by atomic weight (Z - higher

priority groups on the same side)


• For noncyclic: cis is less stable (steric hindrance).

For cyclic, cis more stable.


• Hofmann Rule: Form the least-substituted alkene


• Markovnikof Addition: H adds to C with most -H’s


• Zaitsev Elimination: Form alkene with more





• Dehydrate alcohol (H+, heat) (elimination)


• Dehydrohalogenate haloalkane (base, heat)


• Dehalogenate vic dihalide (Zn, acetic acid)


• Hydrogenate alkyne:


• syn, Z/cis-isomer (H2,P-2 catalyst)


• anti, E/trans-isomer (Li, NH3, -78 ̊C)


• Wittig, aldehyde/ketone + phosphorous ylide




• Combustion (O2)


• Hydrate to 2 ̊/3 ̊ alcohol (H+, H2O); 1 ̊ from ethene;

can rearrange (Markovnikov)


• Hydrate to alcohol; hydroborate/oxidize

(THF/B2H6,H2O2/OH-) (syn, anti-Markovnikov)


• Oxymercurate-demercurate to alcohol


• Hydrohalogenate (HX) (Markovnikov)


• Halogenate (Br2/Cl2), vic dihaloalkane (X2,CCl4; anti)

• Halohydrin (X2, H2O; anti-addition)


• Hydroxylate to form a 1,2-diol (KMnO4, cold OH-syn addition)

• Oxidize to carboxylic acid (KMnO4, hot OH-)


• Ozonolyze to ketone (O3; Zn, H2O)


• Hydrogenate to alkane (Pt, H2; syn-addition)


• Free radical polymerization


• Alkadiene Reaction


• allylic halogenation (Cl2, heat)


• Diels-Alder: cycloalkene from diene + alkene/alkyne

Post By : Pankaj 25 Dec, 2018 2380 views Chemistry