Index of hydrogen deficiency

1. Prepared by
MAHENDRA.G.S
M pharm
Pharmaceutical chemistry
J S S College of Pharmacy
Mysuru
Index of Hydrogen Deficiency (IHD)

2. • The index of hydrogen deficiency is no. of pairs of hydrogen
atom that must be removed from the corresponding “
saturated” formula to produce the molecular formula of the
compound of interest.
• The index of hydrogen deficiency is also called the number of
“ sites(or degree) of unsaturation”;
Index of Hydrogen Deficiency (IHD)

3. • Description is incomplete since hydrogen deficiency can result
from cyclic structures as well as from multiple bonds. The index
is thus the sum of the number of rings, the number of double
bonds, and twice the number of double bonds, and twice the
number of triple bond.
• The index of hydrogen deficiency can be calculated for
compounds containing C,N,H,O,S, and halogen from the
formula .

4. Formula for index hydrogen deficiency
Index= 𝑐𝑎𝑟𝑏𝑜𝑛 −
ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛
2
+
ℎ𝑎𝑙𝑜𝑔𝑒𝑛𝑠
2
+
𝑛𝑖𝑡𝑟𝑜𝑔𝑒𝑛
2
+ 1
• Thus , the compound C7H7NO has an index of 7-3.5+0.5+1=5.
Note that divalent atoms (O,S) are not counted in the formula .
• For the generalized molecular formula αi βii γiii δiv
The index =IV-1/2I+1/2III+1,where .
• α is H,D, or halogen (i.e. any monovalent atom)
• β is O, S, or any other bivalent atom.
• γ is N,P, or any other trivelant atom
• δ is C,Si, or any other tetravalent

5. • The numerals I-IV designate the numbers of
the mono-,di-,tri-,and tetravalent atoms
respectively.
• For simple molecular formulas, we can arrive
at the index by comparison of the formula of
interest With the molecular formula of the
corresponding saturated compound .
• Compare C6H6 and C6H14; The index is 4 for
the formed and 0 for letter

6. The index for C7H7NO is 5 , and a possible structure is
Of course, other isomers( compounds with the same
molecular formula) are possible, such as
Note that the benzene ring itself accounts for four
“sites of unsaturation“ Three for the double bonds
and one for the ring.