Alkenes have one or more double bonds between carbon atoms from "summary" of NCERT Chemistry Class 11 - [CBSE Board] by Dr. S. C. Rastogi, ,Er. Meera Goyal
Alkenes are a type of hydrocarbon that contain one or more double bonds between carbon atoms. This double bond consists of a sigma bond and a pi bond. The sigma bond is formed by the head-on overlap of two sp² hybridized orbitals, while the pi bond is formed by the sideways overlap of two p orbitals. The presence of double bonds gives alkenes certain characteristic properties, such as reactivity towards electrophiles. The general formula for alkenes is CnH2n, where n is the number of carbon atoms in the molecule. This formula indicates that alkenes have a higher degree of unsaturation compared to alkanes, which only contain single bonds between carbon atoms. Due to the presence of double bonds, alkenes can undergo addition reactions in which the pi bond is broken and new atoms or groups are added to the carbon atoms. Alkenes can exhibit geometric isomerism when there are two different groups attached to each carbon of the double bond. In such cases, the restricted rotation around the double bond leads to the formation of cis and trans isomers. The cis isomer has similar groups on the same side of the double bond, while the trans isomer has similar groups on opposite sides of the double bond. The physical properties of alkenes, such as boiling point and melting point, are influenced by factors such as molecular size and shape, as well as intermolecular forces. Alkenes with higher molecular weights tend to have higher boiling points due to increased London dispersion forces between molecules. However, branching in the carbon chain can lower the boiling point by reducing the surface area available for intermolecular interactions. In summary, alkenes are characterized by the presence of one or more double bonds between carbon atoms, which impart unique chemical and physical properties to these hydrocarbons. The double bond structure allows alkenes to participate in various types of reactions and exhibit isomerism, making them important compounds in organic chemistry.
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