H bonding

By Dr. Neelam

1. Presented by
Dr. Neelam
Department of chemistry

2. HYDROGEN BOND
Definition:Itisanelectrostaticattractiveforcebetweencovalently
bondedhydrogenatomofonemoleculeandanelectonegativeatom(F,O,
N)
MainconditionforH-bonding:-
(I)Hshouldbecovalentlybondedwithhighelectronegativeelement
likeF,O,N
(II)Atomicsizeofelectronegativeelementshouldbesmall.
(III)lonepairmustbepresent.
HydrogenbondingoccursinHCN,dueto(-CN)triplebond(sp
hybridisation),electronegativitiesofcarbonandnitrogenincreases.
H F-----------H F--------H F

4. (A)IntermolecularH-bond
H-bondformationbetweentwoormoremoleculesofeitherthesameor
differentcompoundsknownasIntermolecularH-bonding
Thesearetwotypes.
(i)Homointermolecular:-H-bondbetweenmoleculesofsame
compounds.
eg.
(ii)Hetrointermolecular:-H-bondbetweenmoleculesofdifferent
compounds.
eg.alcohol,water

5. (B)IntramoleculaH-bond:-Ittakesplacewithinthemolecule.
(i)H-bondedwithelectronegativeelementsofafunctionalgroup,formH-
bondwithanotherelectronegativeelementpresentonnearestposition
onthesamemolecule.
(ii)ThistypeofH-bondismostlyoccurredinorganiccompounds.
(iii)Itresultinringformation(Chelation).
eg.

6. PropertiesintermolecularH-
bonding
intramolecularH-
bonding
BoilingpointInintermolecularH-
bonding molecular
containVander-Waal
bondingwithH-bonding
InintramolecularH-
bondingmolecular
containVander-Waals
bondingonly
SolubilityIncreasesolubilityin
water.
decreasethesolubility
inwater

7. Properties inter
molecular H-
bonding
intra
molecular H-
bonding
AcidicnatureIncreaseacidic
character
decreaseacidic
character
viscosity Increase decrease

8. PhysicalstateDuetohydrogen
bondingH
2Oisliquid
Duetonotpresentin
hydrogenbondH
2Sis
gas.
Meltingpoint
(H-bond)
H
2O>NH
3>HF
4 4 2
E.N.=F>O>N
(strongerH-bonding
NH
3insolidthanliquid)
BoilingpointH
2O>HF>NH
3
4 24
(strongerH-bondingHF
inliquidorgaseousstate
thaninsolid)

9. Boiling point ∝molecular mass ∝vanderwaalforce
boiling point: HF < H Cl< HBr< HI HCl< HBr< HI < HF
boiling point: H
2O < H
2S < H
2Se < H
2Te H
2S < H
2Se < H
2Te < H
2O
BOND STRENGTH ∝H-bonding ∝E.N. of A ∝
E.N. of B
1
A H --------B
H-bond E.N. atom
E.N. atom
(a)O H------O (b) O H------N
(c) N H------N (d) N H------O
Which has more strength of H-bond

11. 11