Question

Rank substituents in order of their priority when assigning the E or Z label to an alkene.

I, CH2I , H, CH2CH2Cl, F

Answer 1

Concepts and reason

The system used to specify configuration, based on the Cahn-Ingold-Prelog convention, is known as the E-Z system. The relative priorities of the two groups attached to the carbon atom of the double bond are determined in accordance with certain rules called sequence rules. The same process is repeated to determine the relative priorities of the two groups on the other carbon of the double bond. The position of the group of higher priority on one carbon atom is considered relative to the position of the group of higher priority on the other carbon atom. If two groups of higher priority are on the same side of the double bond, the isomer is said to have Z configuration. If the two groups of higher priority are on opposite sides of the double bond, the isomer is said to have E configuration.

Fundamentals

Sequence rules: rules are used to determine the priorities of the groups attached to each carbon of the double bond.

1.The greater the atomic number of the atom directly attached to the carbon, the higher the priority of the group that it is a part of. If different isotopes of the same atom are to be considered, the heavier isotope gets the higher priority.

2.If rule 1 fails to decide upon the relative priority of the two groups attached to a carbon because the first atoms are identical in the two groups, then the rule may be applied by comparing the atomic numbers of the next atom in the groups and

3.When multiple bonds are present, they are treated as separate singles between the atoms concerned.

Atomic number of = 53

Atomic number of = 1

Atomic number of = 9

Among the three, the atom with the highest atomic number is. So, highest priority atom is.

For assigning priorities to the substituents, use rule 2. That is, if the two groups attached to a carbon since the first atoms are identical in the two groups, then the rule may be applied by comparing the atomic numbers of the next atom in the groups.

One of the atoms of a higher atomic number gets a higher priority

has a higher priority than .

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