JEE Main & Advanced Chemistry GOC Inductive Effect Or Transmission Effect

(1) When an electron withdrawing (X) or electron-releasing (Y) group is attached to a carbon chain, polarity is induced on the carbon atom and on the substituent attached to it. This permanent polarity is due to displacement of shared electron of a covalent bond towards a more electronegative atom. This is called inductive effect or simply as I - effect.            

\[C-C-C-C\] Non polar

\[{{C}^{\delta \delta \delta {{\delta }^{+}}}}\xrightarrow{{}}-{{C}^{\delta \delta {{\delta }^{+}}}}\xrightarrow{{}}-{{C}^{\delta {{\delta }^{+}}}}\xrightarrow{{}}-{{C}^{{{\delta }^{+}}}}\xrightarrow{{}}-{{X}^{{{\delta }^{-}}}}\]

\[{{C}^{\delta \delta \delta {{\delta }^{-}}}}-\xleftarrow{{}}\,\,{{C}^{\delta \delta {{\delta }^{-}}}}-\xleftarrow{{}}\ {{C}^{\delta {{\delta }^{-}}}}-\xleftarrow{{}}\,{{C}^{{{\delta }^{-}}}}-\xleftarrow{{}}\,\,{{Y}^{{{\delta }^{+}}}}\]

(2) Carbon-hydrogen bond is taken as a standard of inductive effect. Zero effect is assumed for this bond. Atoms or groups which have a greater electron withdrawing capacity than hydrogen are said to have–I effect whereas atoms or groups which have a greater electron releasing power are said to have +I effect.

\[\xrightarrow[I\text{ }power\text{ }of\text{ }groups\text{ }in\text{ }decreasing\text{ }order\text{ }with\text{ }respect\text{ }to\text{ }the\text{ }referenceH]{CON{{H}_{2}}\,\,>\,\,F\,\,>\,\,Cl\,\,>Br\,\,>\,\,I\,\,>\,\,OH\,\,\,>\,\,\,OR\,\,\,>\,\,N{{H}_{2}}\,\,>\,\,{{C}_{6}}{{H}_{5}}\,\,>H}\]

\[\xrightarrow[+\text{ }I\text{ }power\text{ }in\text{ }decreasing\text{ }order\text{ }with\text{ }respect\text{ }to\text{ }the\text{ }referenceH]{ter.alkyl\text{ }>sec.alkyl\text{ }>pri.alkyl\text{ }>}\] 

\[\xrightarrow[\text{+I power in decreasing order in same type of alkyl groups}]{C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}->C{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}->C{{H}_{3}}-C{{H}_{2}}-}\]

(3) Applications of Inductive effect

(i) Magnitude of positive and negative charges : Magnitude  of +ve  charge  on cations  and magnitude of –ve charge on anions can be compared by \[+I\] or \[–I\]  groups present in it.

Magnitude of \[+ve\] charge \[\propto \frac{1}{+\text{I power of the group}}\propto -I\] power of the group.

Magnitude of \[-ve\] charge \[\propto \frac{1}{-\text{I power of the group}}\propto +I\] power of the group.

(ii) Reactivity of alkyl halide : \[+I\] effect of methyl group enhances \[–I\] effect of the halogen atom by repelling the electron towards tertiary carbon atom.

\[{{H}_{2}}C\to \underset{\begin{smallmatrix}  \uparrow  \\  C{{H}_{3}} \end{smallmatrix}}{\overset{\begin{smallmatrix}  C{{H}_{3}} \\  \downarrow  \end{smallmatrix}}{\mathop{C}}}\,\to X>{{H}_{3}}C\to \underset{{}}{\overset{\begin{smallmatrix}  C{{H}_{3}} \\  \downarrow  \end{smallmatrix}}{\mathop{CH}}}\,\to X\]

\[>C{{H}_{3}}\to C{{H}_{2}}\to X>C{{H}_{3}}\to X\]

Tertiary    >    Secondary   >   Primary  >  Methyl

(iii) Relative strength of the acids :

(a) Any group or atom showing \[+I\] effect decreases the acid strength as it increases the negative charge on the carboxylate ion which holds the hydrogen firmly. Alkyl groups have \[+I\] effect.

Thus, acidic nature is,

\[\xrightarrow[\text{+ I effect increases, so acid strength decreases}]{HCOOH\,\,>\,\,C{{H}_{3}}COOH\,\,>\,\,{{C}_{2}}{{H}_{5}}COOH\,\,>\,\,{{C}_{3}}{{H}_{7}}COOH\,\,>\,\,{{C}_{4}}{{H}_{9}}COOH}\]

Formic acid, having no alkyl group, is the most acidic among these acids.

(b) The group or atom having \[-I\] effect increases the acid strength as it decreases the negative charge on the carboxylate ion. Greater is the number of such atoms or groups (having \[-I\]effect), greater is the acid strength.

Thus, acidic nature is,

\[\xleftarrow[\left( \text{ Inductive effect increases, so acid strength increases} \right)]{\underset{\begin{smallmatrix}\text{Trichloro} \\ \text{acetic acid } \end{smallmatrix}}{\mathop{CC{{l}_{3}}COOH}}\,>\underset{\begin{smallmatrix} \text{Dichloro} \\ \text{acetic acid}\end{smallmatrix}}{\mathop{CHC{{l}_{2}}COOH}}\,>\underset{\begin{smallmatrix} \text{Monochloro} \\ \text{acetic acid} \end{smallmatrix}}{\mathop{C{{H}_{2}}ClCOOH}}\,>\underset{\text{Acetic acid}}{\mathop{C{{H}_{3}}COOH}}\,}\]

(c) Strength of aliphatic carboxylic acids and benzoic acid

\[\underset{\begin{smallmatrix} \uparrow  \\ +I\,\text{group}\end{smallmatrix}}{\mathop{R}}\,\to COOH\,\,\,\,\,\,\,\underset{\begin{smallmatrix} \uparrow  \\ -I\,\text{group}\end{smallmatrix}}{\mathop{{{C}_{6}}{{H}_{6}}}}\,\leftarrow COOH\]

Hence benzoic acid is stronger acid than aliphatic carboxylic acids but exception is formic acid. Thus,

\[\frac{HCOOH\,\,\,>\,\,\,\,\,{{C}_{6}}{{H}_{5}}COOH\,\,>\,\,RCOOH}{\text{Acid strength in decreasing order}}\to \]

• Decreasing order of acids :

\[N{{O}_{2}}C{{H}_{2}}COOH>FC{{H}_{2}}COOH>ClC{{H}_{2}}COOH>BrC{{H}_{2}}COOH\].

\[{{F}_{3}}C-COOH>C{{l}_{3}}C-COOH>B{{r}_{3}}C-COOH>{{I}_{3}}C-COOH\].

\[\underset{\begin{smallmatrix}Methyl \\alcohol\end{smallmatrix}}{\mathop{C{{H}_{3}}OH}}\,>\underset{\begin{smallmatrix}Ethyl \\Alcohol\end{smallmatrix}}{\mathop{C{{H}_{3}}C{{H}_{2}}OH}}\,>\underset{\begin{smallmatrix}Iso-propyl \\alcohol\end{smallmatrix}}{\mathop{{{(C{{H}_{3}})}_{2}}CHOH}}\,>\underset{\begin{smallmatrix}Tert-butyl \\alcohol\end{smallmatrix}}{\mathop{{{(C{{H}_{3}})}_{3}}COH}}\,\].

 As compared to water, phenol is more acidic (\[-I\]effect) but methyl alcohol is less acidic (\[+I\]effect).

(vi) Relative strength of the bases (Basic nature of \[-N{{H}_{2}}\])

The difference in base strength in various amines can be explained on the basis of inductive effect. The \[+I\] effect increases the electron density while \[-I\] effect decreases it. The amines are stronger bases than \[N{{H}_{3}}\] as the alkyl groups increase electron density on nitrogen due to \[+I\] effect while \[ClN{{H}_{2}}\] is less basic due to \[-I\] effect. “So more is the tendency to donate electron pair for coordination with proton, the more is basic nature, i.e., more is the negative charge on nitrogen atom (due to \[+I\]effect of alkyl group), the more is basic nature”.

Thus, the basic nature decreases in the order;

\[\underset{\begin{smallmatrix}\text{Diethyl}\\\text{amine}\end{smallmatrix}}{\mathop{{{({{C}_{2}}{{H}_{5}})}_{2}}NH}}\,>\underset{\begin{smallmatrix}\text{Ethyl} \\\text{amine}\end{smallmatrix}}{\mathop{C{{H}_{3}}C{{H}_{2}}N{{H}_{2}}}}\,>\underset{\begin{smallmatrix}\text{Methyl} \\\text{amine}\end{smallmatrix}}{\mathop{C{{H}_{3}}N{{H}_{2}}}}\,>\underset{\text{Ammonia}}{\mathop{N{{H}_{3}}}}\,>\underset{\begin{smallmatrix}\text{Chloro} \\\text{amine}\end{smallmatrix}}{\mathop{ClN{{H}_{2}}}}\,\]

 The order of basicity is as given below;

• The relative basic character of amines is not in total accordance with inductive effect \[(t>s>p)\] but it is in the following order: Secondary > Primary > Tertiary. The reason is the steric hindrance existing in the t-amines.           
• In gas phase or in aqueous solvents such as chlorobenzene etc, the solvation effect, i.e., the stabilization of the conjugate acid due to \[H\]-bonding are absent and hence in these media the basicity of amines depends only on the +I effect of the alkyl group thus the basicity of amines follows the order : \[{{3}^{o}}>{{2}^{o}}>{{1}^{o}}>N{{H}_{3}}\].            

(vii) Basicity of alcohols : The decreasing order of base strength in alcohols is due to \[+I\] effect of alkyl groups.

\[\underset{({{3}^{o}})}{\mathop{{{(C{{H}_{3}})}_{3}}COH}}\,>\underset{({{2}^{o}})}{\mathop{{{(C{{H}_{3}})}_{2}}CHOH}}\,>\underset{({{1}^{o}})}{\mathop{C{{H}_{3}}C{{H}_{2}}OH}}\,\underset{{}}{\mathop{>C{{H}_{3}}OH}}\,\]

(viii) Stability of carbonium ion : \[+I\] effect tends to decrease the \[(+ve)\] charge and \[-I\] effect tends to increases the \[+ve\] charge on carbocation.

\[{{(C{{H}_{3}})}_{3}}{{C}^{\oplus }}>{{(C{{H}_{3}})}_{2}}C{{H}^{\oplus }}>C{{H}_{3}}CH_{2}^{\oplus }>CH_{3}^{\oplus }\]

(ix) Stability of carbanion : Stability of carbanion increases with increasing \[-I\] effect.

\[CH_{3}^{-}>C{{H}_{3}}CH_{2}^{-}>{{(C{{H}_{3}})}_{2}}C{{H}^{-}}>{{(C{{H}_{3}})}_{3}}{{C}^{-}}\]