Post on 30-May-2018
8/14/2019 Aromatic Hetero Cyclic Compounds
1/14
8/14/2019 Aromatic Hetero Cyclic Compounds
2/14
Review : Aromatic
The structure must be ring structure
Alternating bonds or conjugated bonds.
Follows the Hckel's rule: The number of electrons in the
cyclic system is (4N + 2), with N an integer
The structure must be planar
8/14/2019 Aromatic Hetero Cyclic Compounds
3/14
Ar atic Heter cyclic C p undsy The cyclic part (fr Greek eaning circle) f
heter cyclic indicates that at least ne ring structure is
present in such a c p und.
y prefix heter - (fr Greek eaning ther) refers t the
n ncarb n at s in the ring.
y Heter cyclic c p unds include any f the bi che ical
aterial essential t life. F r exa ple, any naturallyccurring pigments, vitamins, and antibiotics are
heter cyclic c p unds.
8/14/2019 Aromatic Hetero Cyclic Compounds
4/14
Ar atic Heter cyclic C p undsy Aheterocyclic compound is an rganic c p und in
hich ne r re f the carb n at s in the backb ne
f the lecule has been replaced by an at ther than
carb n. Typical hetero atoms include nitr gen, xygen,
and sulfur.
8/14/2019 Aromatic Hetero Cyclic Compounds
5/14
Pyridiney A lecule f pyridine c ntains a ring f six at s five
carb n at s and ne nitr gen at .
8/14/2019 Aromatic Hetero Cyclic Compounds
6/14
Pyrr ley A lecule f pyrr le c ntains a ring f five at s - f ur
at s f carb n ne at f nitr gen.
8/14/2019 Aromatic Hetero Cyclic Compounds
7/14
8/14/2019 Aromatic Hetero Cyclic Compounds
8/14
8/14/2019 Aromatic Hetero Cyclic Compounds
9/14
Nomenclature of heterocyclic
compoundsy The types of heteroatoms present in a ring are indicated by
prefixes; in particular, oxa-, thia-, and aza- denote oxygen,sulfur, and nitrogen atoms, respectively.
y The numbers of heteroatoms of a particular kind areindicated by number prefixes joined to the heteroatom
prefixes, as dioxa- and triaza-.
y The presence of different kinds of heteroatoms is indicated by
combining the above prefixes, using the following order of
preference: oxa- first, followed by thia- and then aza-.
8/14/2019 Aromatic Hetero Cyclic Compounds
10/14
N
ome clat reElement oxyge s lf r sele i m itroge phosphoro s silico boro
Valence II II II III III IV III
Prefix Oxa hia Sele a Aza Phospha Sila Bora
8/14/2019 Aromatic Hetero Cyclic Compounds
11/14
N
ome clat rey I additio , partially sat rated ri gs are i dicated by the
prefixes dihydro-, tetrahydro-, a d so o , accordi g to
the mber of extra hydroge atoms bo ded to theri g atoms.
y
The positio s of heteroatoms, extra hydroge atoms,a d s bstit e ts are i dicated byArabic merals, for
which the mberi g starts at a oxyge atom, if o e is
prese t, or at a s lf r or itroge atom a d co ti es i
s ch away that the heteroatoms are assig ed the lowestpossible mbers.
8/14/2019 Aromatic Hetero Cyclic Compounds
12/14
8/14/2019 Aromatic Hetero Cyclic Compounds
13/14
Synthesis and
modificati
ono
f hetero
cyclicringsy The importantmethods for synthesizing heterocyclic compounds
can be classified under five headings.y Three areways of forming new heterocyclic rings from forerunner
containing either no rings or one fewer ring than the desiredproduct; one is away ofobtaining a heterocyclic ring from another
heterocyclic ring or from a carbocyclic ring; and one involves themodification of substituents on an existing heterocyclic ring.
y In the formation of rings from no ring, the key step is fre uently
the formation of a carbon-heteroatom linkage (CZ, inwhich Zrepresents an atomofnitrogen, oxygen, sulfur, or amore unusual
element). The actual ring closure, however,may involve theformation of a carbon-carbon bond.
8/14/2019 Aromatic Hetero Cyclic Compounds
14/14
Synthesis and
modificati
ono
f hetero
cyclicrings1. Nucleophilic ring closure
2. Electrophilic ring closure
3. Ring closure by way of cyclic transition states
4. Conversion of one heterocyclic ring into another
5. Modification of an e isting ring