basic concepts

Question 1

conjugation

Answer 1

The process of electron density shifting from
one place to another is known as conjugation
in which electron density decreases at one
place and increases correspondingly at some
other place.

Question 2

conjugation explanation

Answer 2

In case of sigma bond, the electron pair is

shared between the two nuclei while in pi-
bond the electron density exists above and

below the bond axis. If it is not able to shift it
is called “localized” e.g. Ethene (CH2 = CH2).
While in compounds having more than 3-p
orbitals on adjacent atoms, may cause
electron shifting as in allyl radical or benzene.

Question 3

conditions for conjugations

Answer 3

1) There must be p-orbitals on 3 adjacent atoms
2) The atoms having p-orbitals must be in same plane

Question 4

characteristics of conjugation

Answer 4

The conjugated ion, radical and molecule are
more stable than non-conjugated system.
 The difference in energy between conjugated
molecule and theoretical unconjugated
molecule (analogue) is called “delocalized or
resonance energy”
 The molecule in which conjugated orbital is
linear are said to be “linear conjugated” molecule while in which it’s branched is called
“cross conjugated”

Question 5

example of conjugation

Answer 5

Some simple organic conjugated molecules are 1,3-butadiene, benzene, and allylic carbocations. The largest conjugated systems are found in graphene, graphite, conductive polymers and carbon nanotubes.

Question 6

hyper conjugation

Answer 6

 The delocalization of sigma electrons with pi
electrons of adjacent double bond is called
hyper conjugation.

Question 7

explanation of hyperconjugation

Answer 7

When carbon to hydrogen bond (C-H) is attached to an unsaturated carbon atom the
electrons of carbon to hydrogen bond (C-H) become less localized by entering into partial
conjugation with attached unsaturated system. It is also mentioned as sigma to pi
conjugation. Thus conjugation between electrons of sigma bong and those multiple
bond is called hyper conjugation.
Above conjugation is also called “no bond
resonance”
 In canonical forms (all resonance hybrids)
where no bond is indicated between carbon
and hydrogen doesn’t mean that there is no
bond. Actually it is weaker than usual carbon
to hydrogen bond and it is proved by
experimental bond length.

 The order of electron donation in hyper
conjugation is as such
CH3- > MeCH2 > Me2CH > Me3C

 The reason is that, hyper conjugation depends
upon hydrogen attached to the α-carbon of
saturated system. It is minimum in tertiary
methyl.

Question 8

example of hyperconjugation

Answer 8

The ethyl cation has 3 C-H σ-bonds that can be involved in hyperconjugation. The more hyperconjuagtion there is, the greater the stabilisation of the system. For example, the t-butyl cation has 9 C-H σ-bonds that can be involved in hyperconjugation

Question 9

steric effect

Answer 9

Effective delocalization via pi orbitals to make
a specific geometrical shape or figure which
allows the molecule to undergo a specific
reaction is called “Steric Effect”

Question 10

explanation of steric effect

Answer 10

 Effect arise in the molecule due to its
geometry that whether a molecule may react
or not
 When the carbon is blocked by all the four
sides the reaction cannot occur. If we ionize
the molecule, then the reaction may occur as
the molecule was blocked from all possible
sides.
 If atoms are not bulky then they can move
within a molecule to allow reaction.
 So geometry is the only thing that allows the
reaction.
 Conjugation, Hyper conjugation, Inductive
Effect and Mesomeric Effect can be modifies
and enhanced in intensity by Steric Effect.

Question 11

example of sterc effect

Answer 11

Molecules like 2-Methylpropan-2-ol have a primary steric effect because they are sterically crowded, which means that the atom in focus (in this case, the central carbon) is surrounded by bulky groups.

Question 12

inductive effect

Answer 12

Inductive effect may be defined as
Polarization of a bond induced by adjacent
polar bond and is denoted by Inductive Effect.
All this happens due to sigma bond.

Question 13

explanation of inductive effect

Answer 13

 Inductive Effect refers to the polarity
produced in a molecule as a result of
difference in electronegativity of different
atoms as compared to one another. In single
covalent bond between unlike atoms, the
electron pair (sigma bond) is attached more
towards more electronegative atoms