{"id":374,"date":"2017-11-14T12:07:21","date_gmt":"2017-11-14T12:07:21","guid":{"rendered":"http:\/\/chemdictionary.org\/?p=374"},"modified":"2017-11-14T12:24:35","modified_gmt":"2017-11-14T12:24:35","slug":"alkene","status":"publish","type":"post","link":"https:\/\/chemdictionary.org\/alkene\/","title":{"rendered":"Alkene"},"content":{"rendered":"

Definition of alkenes<\/h2>\n

Alkenes are hydrocarbons that contain carbon carbon double bond (C=C). The general formula of alkenes are Cn<\/sub>H2n<\/sub> in comparison to alkanes with general formula Cn<\/sub>H2n+2<\/sub>. Alkanes are saturated with hydrogens, while alkenes are two hydrogen less than alkanes. Thus it is known as unsaturated hydrocarbons. For example:<\/p>\n

\"By<\/p>\n

Nomenclature<\/h2>\n

IUPAC system<\/h3>\n

In IUPAC system the alkenes are named by changing the suffix of alkanes \u2013ane to \u2013ene. The steps to write the name of the alkenes are:<\/p>\n

Step 1:<\/em><\/strong> The name of alkenes are started with the name of the longest chain contains the double bond.
\nStep 2:<\/em><\/strong> The numbering of the carbon started from the nearest\u00a0 end carbon of the double bond.
\nStep 3:<\/em><\/strong> The position of the double bond is mentioned by a number before the name of the longest chain hydrocarbon.
\nStep 3:<\/em><\/strong> In case of sustituents the position and name of substituent will then be prefixed to it.
\nFor example:<\/p>\n

\"By<\/h3>\n

Common system<\/h3>\n

In common system the alkenes are named by changing the suffix of alkanes from \u2013ane to \u2013ylene. The nearest end carbon of the double bond in the longest chain is designated as greek letter \u03b1, then the next one \u03b2 and so on.<\/p>\n

Structure<\/h2>\n

The carbon atoms that create double bond, are sp2<\/sup> hybridized. In a double bond, the two carbons are bonded together by overlapping two sp2<\/sup> hybrid orbitals head to head, forming a sigma (\u03c3) bond. The other two sp2<\/sup> orbitals are overlapped with the s orbitals of two hydrogen atoms. The two unhybridized p orbitals of two carbon atoms are overlapped side to side to form \u03c0 bond. Because of the presence of elctron rich \u03c0 bond alkenes are more reactive than alkanes.<\/p>\n

Isomerism<\/h2>\n

Depending on the position of the double bond, position isomers are possible. For example:<\/p>\n

The p orbitals of two carbons overlapped and form a electron cloud above and below the single bond. Thus the rotation around this sigma bond is restricted. Due to this restricted rotation around the double bond, geometrical isomerism is possible in alkenes. For the alkene with general formula RCH=CHR, if the two hydrogens stays in the same side is called cis-isomer and if they are in opposite side is called trans-isomer. For example:<\/p>\n

\"\"<\/p>\n

Physical properties<\/h2>\n