Electronic Effects

Question 1

-I effect

Answer 1

electron withdrawing inductive effect

• group attached to C is more electronegative than C
• partial positive charge formed on C

Question 2

+I effect

Answer 2

electron donating inductive effect

• group attached to C is less electronegative than C
• partial negative charge formed on C

Question 3

Functional groups with -I effect

Answer 3

C-X
C-CX₃
C=O
C-OH
C(=O)H
C(=O)OH
C(=O)R
C-NO₂

Question 4

Functional groups with +I effect

Answer 4

C-Li
C-Mg
C-CH₃
C-R (alkyl group)

Question 5

Inductive Effects

Answer 5

The way in which differences in electronegativity polarise electron density in the sigma framework of a molecule.

Question 6

Reactivity

Answer 6

The movement of electron density to break weak bonds and form new stronger bonds.

Question 7

In heterolytic bond cleavage, the bonding pair moves onto the…

Answer 7

… more electronegative atom.

Question 8

The transistion state is…

Answer 8

… the least stable structure in a reaction step.

Question 9

Hammond Postulate states…

Answer 9

… the transition state of a rection will be similar to the thing it is closest in energy to.

The transisiton state is often similar to the reactive intermediate.

Question 10

Principle of energetically accessible intermediates

Answer 10

The more stable / low energy a reactive intermedtae, the lower the energy barrier to a reaction. The reaction proceeds more rapidly.

Question 11

Mesomeric Effects

Answer 11

The movement of electron density within the pi (double bond and lone pair) system of a molecule via resonance conjugation.

Question 12

Between inductive and mesomeric effects, which has the greatest importance and why?

Answer 12

Mesomeric effects have greater importance.
The electrons in the pi system are more mobile so can move over larger distances.

Question 13

-M effect

Answer 13

Electron withdrawing effect.

-M groups ‘accept’ pairs of electrons

Question 14

+M effect

Answer 14

Electron donating effect

+M groups can donate a pair of electrons

Question 15

Groups with -M effect

Answer 15

Ketone (R-(C=O)-R)
Cyanide (-C≡N)
Nitro (-NO₂)

Groups containing double / triple bonds, particularly to electronegative atoms.

Question 16

Groups with +M effects

Answer 16

-OH (hydroxyl)
-O⁻
-O-R (ether)
-S-R (thioether)
-NR₂ (amine)
-Cl
-Br

Groups with singly bonded atoms holding a lone pair, or groups with a C=C pi bond.

Question 17

Which groups can be +M or -M, depending on what they are bonded to?

Answer 17

Alkenyl (R₂C=C(R)-) and phenyl (C₆H₅).

Question 18

Which effect is responsible for the +I inductive effect of alkyl groups?

Answer 18

Hyperconjugation - bonding electrons from adjacent C-H bonds partially overlap with empty p orbital of carbocation. Partial resonance conjugation donates some electron density to the empty orbital.