isomerism Flashcards
position isomers (ex)
isoemrsim that arises due to difference in postion of same functional group Ex) propan-1-ol, propan-2-ol
functional group isomer
compounds with same moleuclar formula but different functional group Ex) ethanol and dimethylether
metamersim
isomersim that occurs due to unequal distribution of carbon atoms on either side of the functionl groups Ex) pentan-2-ene and pentan-3-ene
structural/constitutional isomer
isomersim due to the different arrangent of atom within a molecule without any reference to space
tautomerism
type of isomerism that occurs due to shifting of proton from one atom to another in same molecule Ex) amino acid and zwitter ion
stereisomer
when isomersim is due to different arrangent of atoms within a molecule with special reference to space.
geometrical isomersim
isomerism that occurs due to restriction of rotation of double bond in acyclic compounds and rotation of single bond in cyclic compounds
chain isomer
type of isomerism that arises to differene in nature of carbon chain Ex) pentane, isopentane, neopentane
restriction in geometrical isomerism
in c-c double bonds the carbon moleule is sp2 hybridized, meaning it has sigma and pi bonds. the presence of pi bonds prevents the molule from rotating.
in cyclic compounds rotation is not possible due to the fact that the ring will break
cis isomers (geometric isomers)
isomer in which two similar groups are on the same side of the double bond ex) cis-2-butane
tran isomers (geometric)
isomers in which two similar groups are on oppisite side of the double bonds Ex) trancs-2-butane
E/Z system
the substituent groups attched to the carbon are all different, so we can use E/Z system to describe this. when equal pritory groups are on the same side it is knows as Z-isomer but if they are on opposite side it is know as E isomer.
properties of geometrical isomerism
stability- trans is more stable becz bulk groups are on opposite sides. in cis isomers there is repulsion between the moluels making it less stable.
inter-conversion- interconversion is only possible if the molcule is heated to a really high temperature or it absorbs light becz this allows bond breakage making rotation about pi-bond possible.
physical-chemical properties- they have same physical propertis but some different chemical propeties
separation- can be separated used convenionl techniques like fractinal distillation or gas chromotography
optical isomers
isomers with the sme molecular formula but are knowns as non-superimpossible mirror images
plane polarized light/ optical activity
plane polarized light- normal light travels in waves in all different directions but when this light is shined through polarized lense it appears to travel in a single wave.
optical activity- the ability of an organi molecule to roatate plane polarized light that is passes through it
optical isomerism
plane polarized light- normal light travels in waves in all different directions but when this light is shined through polarized lense it appears to travel in a single wave.
optical activity- the ability of an organi molecule to roatate plane polarized light that is passes through it
dextro/levo rotatory
dextrorotatory- roates place polarized to the right or clochwise, denoted by d or (+)
levorotatory- roatates plane polarized light to the left or anti clockwise, denoted by l pr (-)
chirality
a carbon atom bonded to different atoms or groups is known as chiral carbon or asymmetric carbo
enatiomers
stereoisomers that are non-superimposable mirror images, when one rotates plane-polarized light to right and one rotates plane polarized light to left and are missor images of each other Ex) 2-bromobutane, lactic acid
properties of enantiomer
-always exist as discrete pair
-always mirror images of each other
-cannot be interconverted under ordinary conditions
-same properties with the exception of rotation of plane polarized lights
-equimolar mixture of two enantiomers is known as racemic mixture
diastereomers
optical isomers that are not mirror images of each other are known as diasteromers
erythrose
isomers having two groups on same side in projection formula
therose form
isomers having two groups on opposit side in projection formula
meso-compound
a compound with 2 or more asymmetric carbon possesing plane of symmertry
R/S system
uses CIP rules for assignment of absolute configaration
-least priority group should be vertical line
R- right or clockwise
S- left or anti-clockwise
D-L notation
D- if OH group is attached to the right
L- if OH group is attached to the left
racemic mixture
an equimolar pair of mixture of enantiomers, and this mixture does not show any optical activity
formation of racemic mixture
mixing of enantiomer- mixing of equal amounts of the two enantiomers
synthesis- synthesis of asymmetrical molecule from symetrical molecule always results in racemic mixture
by addition- Formulation of lactonitrile by the addition of
hydrogen cyanide to acetaldehyde. The cyanide group approaches to the positively
charged carbon atom from front or back which results
in formation of racemic mixture.
by displcement- The formation of alpha bromo proponic acid take
place by Hell-Volhord-Zelinsky
epimers
defined as inversion of configuration at one of the
several center of asymmetry /Chirality.
properties of racemic mixture
in solid state- Mixture: It is simply a mechanical mixture of
two forms dextro and levo. They are known as
conglomerates
It is two phase system. The melting point of racemic
mixture is lower than individual enantiomers
racemic compounds- The molecule of one enantiomer have greater affinity
for the opposite enantiomer this pair unite to
form a molecule called as racemic compound and is
represent one phase system. The physical
properties differ from the constituent enantiomers
In solution form it dissociates into (+) and (-) form.
RACEMIC SOLID SOLUTION
(PSEUDO RACEMIC COMPOUND)
This is known as pseudo racemic compound as there
is a tendency of enantiomers to crystalize together
due to their isomorphic form. They are also 1 phase
system. The arrangement of molecules in the solid is
random and racemic solid solution is obtained.
