Organic Chemistry 3 Flashcards
what are the types of electron displacement effects
The electron displacement in an organic
molecule may take place either in the ground
state under the influence of an atom or a
substituent group or in the presence of an
appropriate attacking reagent. The electron
displacements due to the influence of
an atom or a substituent group present in
the molecule cause permanent polarlisation
of the bond. Inductive effect and
resonance effects are examples of this type of
electron displacements. Temporary electron
displacement effects are seen in a molecule when a reagent approaches to attack it. This
type of electron displacement is called
electromeric effect or polarisability effect.
what is inductive effect
the displacement of sigma- electrons along a saturated carbon chain whenever an electron donating/ electron withdrawing groyp is present at the end of the chain is called as inductive effect. Inductive effect decreases steadily with increasing distance from the e- withdrawing/donating group and becomes negligible after three carbon atoms.
It takes place in the ground state of the cpd hence it is a permanent effect.
Magnitude of inductive effect diminishes
as the number of intervening bonds
increases.
explain inductive effect with example
C4- c3- c2-c1- X
consider a carbon chain that is connected to an electron withdrawing group/atom like a halogen.
The sigma electrons b/w c1 and x are displaced towards x because it is more electronegative. hence it aquires a small delta - charge while the c1 atom acquires a small delta + charge.
The c1 atom with delta+ charge will attract the sigma e-s of c1-c2 bond, hence the c2 atoms qcquires a delta delta + charge. This charge is smallee than +ve charge on c1 atom
what are the 2 types of inductive effect
i) -I effect
if the substituent present at the end of the chain is electron withrawing
NO2> CN> COOH> F> Cl> Br>I
ii)+I effect
if the substituent present at athe end of the chain is electron donating
alkyl gropus
what is electromeric effect
It is a temporary effect. The organic
compounds having a multiple bond (a double
or triple bond) show this effect in the presence
of an attacking reagent only.
It is defined as
the complete transfer of a shared pair of
π-electrons to one of the atoms joined by a
multiple bond on the demand of an attacking
reagent.
As soon as the reagent is removed from the domain of the reaction, the molecule reverts back to its original form.
what are the 2 types of electromeric effect
(i) Positive Eelctromeric Effect (+E effect) In
this effect the π−electrons of the multiple bond
are transferred to that atom to which the
reagent gets attached.
eg: addition of acid to alkene
ii)Negative Electromeric Effect (–E effect) In
this effect the π - electrons of the multiple
bond are transferred to that atom to which
the attacking reagent does not get attached
addition of cn- to carbonyl grp
tip: unsaturated systems show +e with electrophiles and -e effect with nucleophiles
Hyperconjugation/ Baker Nathan effect/ No bond resosnance
Hyperconjugation is a general stabilising
interaction. It involves delocalisation of
σ electrons of C—H bond of an alkyl group
directly attached to an atom of unsaturated
system or to an atom with an unshared
p orbital. The σ electrons of C—H bond of the
alkyl group enter into partial conjugation with
the attached unsaturated system or with the
unshared p orbital. Hyperconjugation is a
permanent effect.
In general, greater the number of alkyl
groups attached to a positively charged carbon
atom, the greater is the hyperconjugation
interaction and stabilisation of the cation.
what are canonical/resonance structures ? what is resonance?
Resonance is said to occur when a molecule, when we can write two or more lewis structures that differ inthe position of electrons but not in the relative position of atoms.
The various lewis structures, none of are sufficient to explain all the properties of the compound accurately are called canonical/resonance structures.
The resonance structures
(canonical structures or contributing
structures) are hypothetical and
individually do not represent any real
molecule. They contribute to the actual
structure in proportion to their stability.
The actual molecule is represented by the resonance hybrid of the various canonical structure.s
what is resonance energy
The
difference in energy between the actual
structure and the lowest energy resonance
structure is called the resonance
stabilisation energy or simply the
resonance energy. The more the number of
important contributing structures, the more
is the resonance energy.
which resonating structure is more stable
Among the resonance
structures, the one which has more number
of covalent bonds, all the atoms with octet of
electrons (except hydrogen which has a
duplet), less separation of opposite charges,
(a negative charge if any on more
electronegative atom, a positive charge if any
on more electropositive atom) and more
dispersal of charge, is more stable than others
define resonance effect/mesomeric effect
The resonance effect is defined as ‘the polarity
produced in the molecule by the interaction
of two π-bonds or between a π-bond and lone
pair of electrons present on an adjacent atom’.
The effect is transmitted through the chain.
There are two types of resonance or
mesomeric effect designated as R or M effect.
what are the 2 types of resonance effect
(i) Positive Resonance Effect (+R effect)
In this effect, the transfer of electrons is away
from an atom or substituent group attached
to the conjugated system. This electron
displacement makes certain positions in the
molecule of high electron densities.
(ii) Negative Resonance Effect (- R effect)
This effect is observed when the transfer of
electrons is towards the atom or substituent
group attached to the conjugated system.
what is a conjugated system
The presence of alternate single and
double bonds in an open chain or cyclic
system is termed as a conjugated system.
what are the types of organic reactions
Organic reactions can be classified into the
following categories:
(i) Substitution reactions
(ii) Addition reactions
(iii) Elimination reactions
(iv) Rearrangement reactions
what are substitution reactions
the reaction in whcih hydrogen or any functional group is substituted by another atom/group
CH3CH2Br + KOH—-> CH3CH2OH+ KBr
