JEE Main & Advanced Chemistry Organic Chemistry: Some Basic Principles & Techniques Alkyl groups

Alkyl groups

Category : JEE Main & Advanced

These are univalent groups or radicals obtained by the removal of one hydrogen atom from a molecule of a paraffin. The symbol 'R' is often used to represent an alkyl group.

           \[\begin{align}   & \text{(Alkane) }{{C}_{n}}{{H}_{2n+2}}\xrightarrow{-H}{{C}_{n}}{{H}_{2n+1}}\text{ (Alkyl group)} \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(R-H)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(R-) \\ \end{align}\]           

Alkyl groups are named by dropping-ane from the name of corresponding paraffin and adding the ending'yl.

Parent saturated hydrocarbon Name of the alkyl group Structure
Methane Methyl \[C{{H}_{3}}-\]
Ethane Ethyl \[C{{H}_{3}}-C{{H}_{2}}-\]
Propane n-Propyl \[C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-\]
Butane n-Butyl \[C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-\]

Alkyl groups derived from saturated hydrocarbons having three or more carbon atoms exist in isomeric forms.

Similarly, removal of different H atoms in pentane gives the following radicals :           

\[\underset{n-Pentyl}{\mathop{C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}-}}\,\];\[\underset{\text{Isopentyl}}{\mathop{\underset{C{{H}_{3}}\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{\underset{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{3}}CHC{{H}_{2}}C{{H}_{2}}-}}\,}}\,}}\,\]; \[\underset{\text{Neopentyl}}{\mathop{\underset{\,\,\,\,\,\,C{{H}_{3}}}{\mathop{\underset{|\,\,\,}{\mathop{\overset{\,\,\,\,C{{H}_{3}}}{\mathop{\overset{|\,\,\,\,}{\mathop{C{{H}_{3}}CC{{H}_{2}}-}}\,}}\,}}\,}}\,}}\,\];\[\underset{\sec -\text{Pentyl}}{\mathop{\underset{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{3}}CHC{{H}_{2}}C{{H}_{2}}C{{H}_{3}}}}\,}}\,\]; \[\underset{tert-\text{Pentyl}}{\mathop{\overset{\text{C}{{\text{H}}_{\text{3}}}\,\,\,\,}{\mathop{\underset{|\,\,\,\,\,\,\,\,}{\mathop{\overset{|\,\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{3}}CC{{H}_{2}}C{{H}_{3}}}}\,}}\,}}\,}}\,\] Unsaturated groups or radicals

Group Common name IUPAC name
\[C{{H}_{2}}=CH-\] Vinyl Ethenyl
\[C{{H}_{2}}=\overset{2}{\mathop{C}}\,H-\overset{1}{\mathop{C}}\,{{H}_{2}}-\] Allyl 2-Propenyl
\[C{{H}_{3}}-CH=\overset{1}{\mathop{C}}\,H-\] - 1-Propenyl
\[HC\equiv C-\] Acetylide Ethynyl
\[HC\equiv \overset{2}{\mathop{C}}\,-\overset{1\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{2}}}}\,-\] Propargyl 2-Propynyl

   



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