General Organic Chemistry

Hydrogen bonding occurs when a molecule has a hydrogen atom bonded to a highly electronegative atom like N, O, or F - and there is a lone pair on another N,O, or F atom that can participate in bonding.
1. Ethanol (CH3CH2OH)
Has an - OH group
Can form hydrogen bonds ( O−H⋯O )
2. Acetic acid (CH3COOH)
Has both C=O and - OH groups
Forms strong hydrogen bonds (dimers, intramolecular and intermolecular H-bonding possible)
3. Ethylamine (CH3CH2NH2)
Has an −NH2 group
Can form hydrogen bonds ( N−H⋯N or N−H⋯O with other molecules)
4. Trimethylamine ((CH3)3N)
Has nitrogen with a lone pair but no N−H bond
Cannot form H-bonds as donor, though it can accept them - but "having H-bonding" typically means being capable of intermolecular H -bonding as both donor and acceptor. Since it cannot donate an H , we generally do not count it as hydrogen-bonding on its own.
5. Salicylic acid (o-hydroxybenzoic acid)
Has both - OH and - COOH groups; strong intramolecular hydrogen bond and intermolecular as well.
H-bonding present
6. Ethanal ( CH3CHO )
Has a C=O group only, no - OH or −NH−
Cannot form hydrogen bonds with itself (can accept H bonds but not donate).
Substances with H-bonding:
Ethanol
Acetic acid
Ethylamine
Salicylic acid
Total =4