eLFH - Molecular Structure and Isomerism Flashcards
Isomerism definition
Existence of 2 or more substances composed of the same elements, in the same proportions, but with variations in the arrangement of atoms
Variations lead to different chemical properties
Types of Isomers
Main 2 categories are Constitutional (aka structural) isomers and Stereoisomers
Common anaesthetic drugs with isomers
Bupivacaine and Levobupivacaine
Ketamine and (S) ketamine
Atracurium and Cisatracurium
Enflurane and Isoflurane
Midazolam (open ring and closed ring forms)
Enflurane and Isoflurane isomer structures
Tautomer definition
Organic compounds that are interconvertible by a chemical reaction called tautomerization
Usually involves migration of hydrogen atom and switch of a single bond and adjacent double bond
Example of tautomer
Midazolam
Buffered preparation (pH 3.5) water based solution in open ring form suitable for IV use
At body pH (or when pH > 4) becomes closed ring form, more lipid soluble and able to penetrate CNS
Aromatic isomer definition
Type of constitutional isomer
Chemical group bonded to different position on benzene ring
Enantiomer definition
Type of stereoisomer
Same atoms connected in same order but different 3D arrangement
Non-superimposable mirror images of each other
Occurs when there is a carbon atom bonded to 4 different atoms / functional groups
Old categories for Enantiomers
According to direction of deflection of polarised light
Left deflection - Laevo or L forms
Right deflection - Dextro or D forms
New categories for Enantiomers
Based on distribution of groups around chiral centre
Left handed - (S) configuration
Right handed - (R) configuration
Racemic mixture definition
Mixture of equal (S) and (R) enantiomers
Enantiomers may have different affinities for receptors
Diastereomer definition
Molecule has more than one chiral centra and the spatial configuration is different only around a subset of the chiral centres
Types of Diastereomers
Cis-trans
Conformers
Cis-trans isomers
Carbon-carbon double bond cannot rotate
When substituted groups are on same side of double bond then called Cis isomer
When groups are on different sides of double bond then called trans isomer
Examples of cis isomers
Atracurium and Cisatracurium
