Electronic effects inductive,mesomeric,electromeric

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2. ELECTRONIC EFFECTS INDUCTIVE EFFECT , MESOMERIC EFFECT ELECTROMERIC EFFECTS BY -Neha Tripathee Assistant Professor K.M.G.G.P.G.COLLEGE BADALPUR B.Sc.I .PAPER II,UNIT II

3. Inductive Effect The  inductive effect  is a permanent state of polarization. The electron density in a  bond between two unlike atoms is not uniform. The inductive effect is a distance-dependent phenomenon The inductive effect is permanent, but relatively weak, and can be easily overshadowed by the electronic effects discussed later.

4. There are two categories of inductive effects: the  electron-withdrawing (-I effect ) and the  electron-releasing (+I effect). –NH 3 +  > –NO 2  > –SO 2 R > –CN > –SO 3 H > –CHO > –CO > –COOH > – COCl > –CONH 2  > –F > – Cl > –Br > –I > –OH > -OR > -NR 2  > –NH 2  > –C 6 H 5  > –CH=CH 2  > –H The strength of inductive effect is also dependent on the distance between the substituent group and the main group that react; the greater the distance, the weaker the effect.

5. Applications- The inductive effect is used to tell the stability of the ion. STABILITY OF ION α 1/CHARGE DENSITY The inductive effect can be used to determine the stability of a molecule depending on the charge present on the atom and the groups bonded to the atom. For example if an atom has a negative charge and is attached to a + I group its charge becomes 'amplified' and the molecule becomes more unstable .

6. CONT…. If an atom has a negative charge and is attached to a - I  group its charge becomes 'de-amplified' and the molecule becomes more stable than if I-effect was not taken into consideration. STABILITY OF CARBOCATION - tertiary carbocation > secondary carbocation >primary carbocation > methyl carbocation

7. STRENGTH OF CARBOXYLIC ACID It   depends on the extent of its ionisation , The more ionized is it, the stronger it is. As an acid becomes stronger, the numerical value of its pKa  drops. Thus Acetic acid < formic acid < chloro aceic acid And mono chloro acetic acid< dichloro acetic acid<tri chloro acetic acid

8. Comparison between inductive effect and electromeric effect Inductive Effect Electromeric Effect The polarization of a single σ covalent bond due to the electronegativity difference between the bonding atoms is called the inductive effect It is a permanent effect It doesn't need the presence of a reagent Induced charges appear as partial charges(∆+ or∆−) The complete shift of the π bond electron pair of a double or triple bond to one of the atoms joined by it, in the presence of a suitable electrophilic reagent, is called the electromeric effect It is a temporary effect It needs the presence of an electrophilic reagent Induced charges are integral: +1 or −1

9. ELECTROMERIC EFFECT- This effect is shown by those compounds containing multiple bonds. When a  double bond  or  triple bond  is exposed to an attack by a  reagent , a pair of bonding electrons involved in the pi bond is transferred completely from one atom to another. This effect will remain as long as the attacking reagent is present. As soon as the reagent is removed, the polarized molecule will come back to the original state.

10. +E and -E groups Electromeric effect can be classified into +E and -E effects based on the direction of transfer of the electron pair. When the electron pair moves towards the attacking reagent, it is termed as the +E effect . The addition of acids on alkene  is an example of the +E effect. The -E effect can be found in reactions such as addition of nucleophiles to carbonyl compounds.

11. MESOMERIC EFFECT- The concepts of mesomeric effect, mesomerism and mesomer were introduced by Ingold in 1938 as an alternative to Pauling's synonymous concept of resonance.[1] " Mesomerism " in this context is often encountered in German and French literature, but in English literature the term "resonance" dominates. Mesomeric effect can be transmitted along any number of carbon atoms in a conjugated system. This accounts for the resonance stabilization of the molecule due to delocalization of charge.

12. EFFECT ORDER : +M –O −  > –NH 2  > –NHR > –OR > –NHCOR > –OCOR > –Ph > –F > – Cl > –Br > –I - M –NO 2  > –CN > --HSO 3 > –CHO > –C=O > –COOCOR > –COOR > –COOH > –CONH 2  > –COO −  

13. MESOMERIC EFFECT IS A PERMANENT EFFECT AS THE INDUCTIVE EFFECT. IT OPERATES IN COMPOUNDS WHERE THER IS CONJUGATION ,I.e. PAI BOND AND SIGMA BOND BOTH ARE THERE. IT IS RESPONSIBLE FOR MORE THAN ONE RESONANCE HYBRID STRUCTURES OR MESOMERIC FORMS OF THE COMPOUND.