C H Bond Strengths

Overview

CH bond strengths depend on:
- Hybridization of the carbon atom
- Type of molecule
Bond strengths ranked from strongest to weakest based on bond dissociation energies (BDE).

Type of CH Bond	Hybridization of C	Bond Dissociation Energy (BDE)	Relative Strength
Alkyne CCH (terminal)	sp	~530 kJ/mol	Strongest
Alkene C=CH (vinyl)	sp	~460-470 kJ/mol	Strong
Aromatic CH (e.g., benzene)	sp	~460 kJ/mol	Strong
Alkane CH (primary)	sp	~410 kJ/mol	Moderate
Alkane CH (secondary)	sp	~398 kJ/mol	Slightly weaker
Alkane CH (tertiary)	sp	~390 kJ/mol	Weaker
Benzylic / Allylic CH	sp (resonance)	~360-370 kJ/mol	Weak

Stronger bonds have higher BDE
- More energy required to break the bond
Hybridization Trend:
- sp > sp > sp in terms of bond strength
- Due to greater s-character, electrons are more tightly held.
Resonance-Effects:
- Resonance-stabilized radicals (such as allylic or benzylic) correspond to weaker CH bonds.