ISOMERISM Flashcards
What are the 3 sub-groups of constitutional isomers
Chain isomers: the same molecular formula but differ in the order in which the carbon atoms are bonded
Positional isomers: same molecular formula but differ in the position of a functional group on the carbon chain
Functional isomers: same molecular formula but possess different functional groups
What is a stereoisomer
molecules which contain the same numbers and types of atoms, all bonded to each other in the same order, with the only difference between the molecules being that some bonds and, therefore, atoms are arranged differently in space
When depicting molecules what do the following symbols mean:
Straight lines:
Wedges:
Dashes:
Straight Lines: bond in the plane
Wedges: bonds projecting towards viewer (coming out of the plane)
Dashes: bonds projecting away from viewer (behind the plane)
The more staggered the atoms are…
The more stable they are
Are cis or trans isomers more stable? why?
Cis alkenes are less stable than trans isomers - because of steric interference between the large substituents in the same side of the double bond
Explain cis and trans isomers on a ring
Cis: on the same side of the ring
Trans: on the opposite side of the ring
(more of an up and down structure not side to side)
What is an E and a Z isomer?
For cis and trans isomers that are tri- and tetra- substituted alkenes
E: if the higher priority groups on each C are on opposite sides of the double bond, the alkene is designated E
Z: If the higher priority groups on each C are on the same side of the double bond, the alkene is designated Z
Explain chirality
Carbons with 4 different groups attached are referred to as chiral
Chiral centres only have single bonds
All chirocentres are stereocentres
What is an enantiomer
The mirror image of a chiral compound, it is nonsuperimposable and a different compound
What is a stereocentre?
A stereocentre is an atom bearing groups that may be interchanged leading to a stereoisomer
Stereocentres can have double or single bonds
all chirocentres are stereocentres but not the other way around
Define ‘Achiral’
A molecule that IS superimposable in its mirror image is achiral
An object or molecule is achiral if it has a plane of symmetry
What are the similarities and differences in physical properties of enantiomers
identical chemical and physical properties in an churl environment (MP, BP, solubility, chemical reactivity, spectra)
Different physical properties in chiral environments (e.g., in the body)
enantiomers rotate the plane of light in the same magnitude, but in opposite directions
How to assign molecule priorities on enantiomers
Priority is assigned according to atomic number. The highest atomic number assigned is the highest priority. In case of ties, keep going along the chain
What are R and S priorities?
How do you determine priorities?
R: clockwise
S: anticlockwise
Priorities are determined and then the lowest priority is put at the back and the other 3 are rotated
What are diastereomers?
What is the formula to determine the max amount of stereoisomers?
diastereomers are configurational stereoisomers that are not enantiomers (not mirror images)
diastereomers have 2 or more stereogenic centres
They have some matching, some opposite configurations
Maximum number of stereoisomers in 2^n, where n = the number of chiral carbons
