goc 1 Flashcards
what are electrophiles
- attak region with high e- density
-they accept electron pair from substrate and form coordinate bond
-may be +vely charge or neutral molecules
-lewis acid
what are the types of electrophile
Positively charged electrophiles :
H+, SO3H+, NO+,NO2+,COOH+, X+,R+
(ii) Neutral electrophiles :- central atom e– deficient
(a) All Lewis acids as :
BF3
, AlCl3
, SO3, ZnCl2
, BeCl2
, FeCl3
, SnCl2
, CO2, SnCl4
(b) Free radicals, carbenes and nitrenes act as electrophiles.
what are nucleophiels
- -attack the site of low e- density
- they donate pair of e-s to the substrate and form coordinate bond
-maybe -vely charged or neutral
-lewis base
-possess atom with lone pair of e-s
what are the types of nucleophiles
(i) Negatively charged
H-, OH-, OR-, CN-,X-, R -COO-, ,R-, NH2-
(ii) Neutral molecules with lone pairs and pi e-s
H2O, HOR, ROR, NH3, NH2-R, NR3
(iii)Ambident nucleophile :- Nucleophiles which have two sites of electron rich centre or in which two or more
atoms bear a lone pair of electrons.
Examples :-
K+ O—N=O,
NH2–OH,
NaCN
Reaction intermediate: carbocation/carbonium ion
Cation in which positive charge is present on carbon atom is called carbocation.
Due to electron deficiency it acts as an electrophile and always attack on electron richer site.
It is incomplete octet species because it has six electron in outer most shell.
All electrons are paired.
has sp2 hybridisation and trigonal planar
Reaction intermediate: Carbanion
Anion in which negative charge is present on carbon atom is called carbanion.
It has eight electron in outermost shell so it is complete octet species.
It is an electron richer species because it has extra electron.
Due to presence of non bonding electrons it acts as a nucleophile.
has sp3 hybridisation and trigonal pyrmaidal
Reaction intermediate: Ccarbon free radicl
Electrically neutral species in which unpaired electron is present on carbon atom is known as carbon free
radical.
It has seven electron or odd electron in outermost shell.
It is incomplete octet species so it is also electron deficient species.
Reaction Intermediate: Carbene
Carbenes are neutral carbon species in which the carbon atom is bonded to two monovalent atoms or groups
and carries two nonbonded electrons.
It behaves as an electrophile.
It is neutral.
It has 6 e-s. It has 4 bonded, 2 free e-s
Reaction Intermediate: Nitrene
Nitrenes are neutral nitrogen species in which the nitrogen is bonded to one monovalent atom or group and
carries four non-bonded electrons.
It is monovalent radical.
It is neutral.
6 e– in outermost shell.
Two are bonded and four are nonbonded electrons.
two types of carbene
-singlet carbene
-triplet carbene
what is inductive effect
-it is the displacement of e-s toward the more electornegative atom
due to this polarity is induced in the bond
This effect is passed on to the subsequent
bonds also but the effect decreases rapidly
as the number of intervening bonds increases
and becomes vanishingly small after three
bonds. The inductive effect is related to the
ability of substituent(s) to either withdraw or
donate electron density to the attached carbon
atom
what is mesomeric effect
delocalisation of pi e-s from shell to shell is called as resonance or mesomeric effect
wgat are op directing grps
what are m -directing grps
The +M grps are op directing grps. They increase e- density at ortho/ para position and hence called so
the -M grps are called meta directing grps because they decrease e- density at ortho/para posiition and hence indirectly increasing e- density in meta posn
what is hyperconjugation
Complete transfer of e– of C–H sigma bond towards p bond or positive charge or free electron is called as
H-effect (permanent effect). It is also called as No bond resonance and given by Nathen and Baker.
this takes place only i =f there is carbocation, double bond/triple bond and free radical. no hyoercnjugation in carbanion
