Which of the following will have the highest priority if we are considering E and Z nomenclature of geometrical isomers?
Which of the following will have the highest priority if we are considering E and Z nomenclature of geometrical isomers?
The correct option is A -I
Do you remember the sequence rules for determining the priority order?
Let's take a look.
(i) Higher priority is assigned to the atoms of higher atomic number. For example, the order of precedence in the following atoms, H, Cl, I, Br is: I (at. No. 53) > Br (at. No 35) >Cl (at. No 17) > H (at. No 1)
(ii) If isotopes of the same element are attached, the isotope with higher mass number is given higher order of precedence. For example, deuterium is assigned higher priority in comparison to hydrogen
..
(iii) In the groups, the order of precedence is also decided on the basis of atomic number of fist atom of the group. For example, in the following set, -Cl -OH, -COOH, -NH −CH3 ,−SO3H
The order of the precedence is:
When the order of precedence of the groups cannot be settled on the first atom, the second atom or the subsequent atoms in the groups are considered. For example, in the set−CH2 −CH3,−CH3,−COOH, the order cannot be decided on the basis of first atom as it is same in the entire group. However, in −CH2 −CH3, the second atom is carbon, in −CH3, the second atom is hydrogen while in -COOH, the second atom is oxygen. Hence, the order of precedence is:
(iv) A doubly or triply bonded atom is considered equivalent to two or three such atoms. For example,
The group 
is equal to 
and the group -C ≡ N is equal to 
Here, the highest atomic number is of -I.
So, highest priority will be of I.
-I
Do you remember the sequence rules for determining the priority order?
Let's take a look.
(i) Higher priority is assigned to the atoms of higher atomic number. For example, the order of precedence in the following atoms, H, Cl, I, Br is: I (at. No. 53) > Br (at. No 35) >Cl (at. No 17) > H (at. No 1)
(ii) If isotopes of the same element are attached, the isotope with higher mass number is given higher order of precedence. For example, deuterium is assigned higher priority in comparison to hydrogen..
(iii) In the groups, the order of precedence is also decided on the basis of atomic number of fist atom of the group. For example, in the following set, -Cl -OH, -COOH, -NH −CH3 ,−SO3H
The order of the precedence is:
When the order of precedence of the groups cannot be settled on the first atom, the second atom or the subsequent atoms in the groups are considered. For example, in the set−CH2 −CH3,−CH3,−COOH, the order cannot be decided on the basis of first atom as it is same in the entire group. However, in −CH2 −CH3, the second atom is carbon, in −CH3, the second atom is hydrogen while in -COOH, the second atom is oxygen. Hence, the order of precedence is:
(iv) A doubly or triply bonded atom is considered equivalent to two or three such atoms. For example,
The group is equal to and the group -C ≡ N is equal to
Here, the highest atomic number is of -I.
So, highest priority will be of I.
