1) Geometrical isomerism arises when groups are arranged differently in space due to restricted bond rotation. 2) Cis-isomers have similar groups on the same side of a double bond, while trans-isomers have them on opposite sides. 3) Factors like boiling point, melting point, and dipole moment differ between cis and trans isomers due to their structural differences.

1. PHARMACEUTICAL
ORGANIC CHEMISTRY –III
TOPIC: Geometrical Isomerism& its
nomenclature
Represented by: Ishika Choudhary
B.Pharma; 2nd year
Enrollment no.-AJU190857
Roll no.-51
ARKA JAIN UNIVERSITY, Jamshedpur, Jharkhand.
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2. GEOMETRICAL ISOMERISM (GI)
The geometrical isomerism arises
when atoms or groups are arranged
differently in space due to
restricted rotation of a bond or
bonds in a molecule.
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4. NOMENCLATURE OF GI :-
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5. Isomer in which similar groups or atoms lie
on the same side of double bond are called
cis-isomer where as isomers in which similar
groups lie on the opposite side of double
bond are called trans-isomer.
Cis-Trans Nomenclature :-
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6. Factors affecting cis-trans isomers:-
1) The molecule must have a C - C double
bond.
2) Two atoms or groups attached to doubly
bonded carbon atom must be different.
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7. 3) Boiling point : Cis isomer have higher boiling point due to dipole-
dipole interaction.
Trans isomer have comparatively low boiling point
4) Melting point: Cis-isomer has lower melting point because the
structure is not symmetrical
Due to symmetry, trans isomer fits better in crystal lattice, thus has
higher lattice energy and hence higher melting point.
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8. 5) Dipole moment : In cis isomer, dipole moment of polar groups have
additive effect thus have higher dipole moment than corresponding
trans isomer.
In trans isomer, dipole moment of polar groups have opposing effect,
thus tends to cancel each other
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9. NOTE :-
1) Ring have less than 8 members, double bond will be
always cis-isomer.
2) In 8,9,10 members ring, cis isomer will be more stable.
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10. 3) In 11 or more member ring, trans-isomer will be more stable.
4) If even number of double bond or ring is present, it will NOT
show Geometrical Isomerism (GI).
Eg,.a)
b)
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11. 5) If odd number of double bonds or rings are present, it may show GI.
Eg,.a) or
b)
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12. E-Z nomenclature :-
• In this system we assign a priority to the groups
attached to double bonded carbon atom. If groups
of similar priority lie on the similar side of double
bond, the isomer is designated as Z ( Zusammen,
means together). If groups of similar priority lie on
the opposite side of double bond, the isomer is
designated as E ( Entgegen, means opposite)
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14. SEQUENCE RULES:-
The following rules are followed for deciding the precedence order of
the atoms or groups:
(i) Higher atomic number atoms get higher priority.
(ii) Among the isotopes of same element, isotope of higher mass is
given higher priority. Eg,.The Deuterium isotope (H2 or D) has more
priority than protium (H1 or H).
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15. (iii) In the groups, the order of precedence is also decided on
the basis of atomic number of first atom of the group.
(iv) A double or triple bonded atom is considered equivalent
to two or three such atoms, For example;the group >C=O is
equal to and the
group.
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16. (v) If one of the position is occupied by lone pair, it is given least
priority over the bonded group.
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17. The oximes are formed when carbonyl compounds are treated with hydroxyl amine.
These are represented as:
Where R & R1 are hydrogens; or alkyl or aryl groups.
The oximes are of two types:
1) Aldoximes: These are derived from aldehydes. In this case, at least either R or R1 is
hydrogen.
2) Ketoximes: These are derived from ketones. In this case, both R or R1are alkyl or
aryl groups only.
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Syn- anti Configuration

18.  The oximes show geometrical isomerism due to restricted
rotation of C=N bond. Two geometrical forms are possible for
the oximes as shown below.
Eg,.syn and anti oximes
 In case of aldoximes, the syn form is the one in which both the
hydrogen and the hydroxyl (-OH) group are on the same side of
the C=N. Whereas in the anti form, they are on the opposite
side.
E.g. The syn and anti forms of acetaldoxime are shown below.
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19. KETOXIMES :-
• ketoxime of butanone can be named as either syn
methyl ethyl ketoxime or anti ethyl methyl ketoxime:-
a) With respect to methyl
and hydroxyl group ,as
both are on the side .
Therefore called syn-
methyl ethyl ketoximes.
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20. b) With respect to ethyl and
hydroxyl group , as both are in
opposite side. Therefore, called
anti-ethyl methyl ketoximes.
But,
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