ISOMERISM Flashcards

1
Q

What are the 3 sub-groups of constitutional isomers

A

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

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2
Q

What is a stereoisomer

A

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

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3
Q

When depicting molecules what do the following symbols mean:
Straight lines:
Wedges:
Dashes:

A

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)

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4
Q

The more staggered the atoms are…

A

The more stable they are

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5
Q

Are cis or trans isomers more stable? why?

A

Cis alkenes are less stable than trans isomers - because of steric interference between the large substituents in the same side of the double bond

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6
Q

Explain cis and trans isomers on a ring

A

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)

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7
Q

What is an E and a Z isomer?

A

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

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8
Q

Explain chirality

A

Carbons with 4 different groups attached are referred to as chiral

Chiral centres only have single bonds

All chirocentres are stereocentres

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9
Q

What is an enantiomer

A

The mirror image of a chiral compound, it is nonsuperimposable and a different compound

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10
Q

What is a stereocentre?

A

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

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11
Q

Define ‘Achiral’

A

A molecule that IS superimposable in its mirror image is achiral

An object or molecule is achiral if it has a plane of symmetry

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12
Q

What are the similarities and differences in physical properties of enantiomers

A

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

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13
Q

How to assign molecule priorities on enantiomers

A

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

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14
Q

What are R and S priorities?

How do you determine priorities?

A

R: clockwise
S: anticlockwise

Priorities are determined and then the lowest priority is put at the back and the other 3 are rotated

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15
Q

What are diastereomers?

What is the formula to determine the max amount of stereoisomers?

A

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

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16
Q

What is a meso compound?

A

an achiral compound with 2 or more stereocentres

doesn’t fit the 2^n rule for the number of possible stereoisomers

Generally contain a plane of symmetry

17
Q

What is a polarimeter

A

an instrument used to measure how far molecules rotate the plane of polarised light

18
Q

What is a racemic mixture?

A

A racemic mixture contains an equal amount of the 2 enantiomers

19
Q

define resolution and asymmetric synthesis in enantiomers

A

resolution: synthesising a racemic mixture of the drug and then separate the 2 enantiomers

Asymmetric synthesis: controlling the synthetic conditions so only 1 enantiomer is predominantly formed