Unreactivity of Alkanes
Strength of C-H bonds
- Alkanes consist of carbon and hydrogen atoms which are bonded together by single bonds
- Unless a lot of heat is supplied, it is difficult to break these strong C-C and C-H covalent bonds
- This decreases the alkanes’ reactivities in chemical reactions
Lack of polarity
- The electronegativities of the carbon and hydrogen atoms in alkanes are almost the same
- This means that both atoms share the electrons in the covalent bond almost equally
The Pauling Scale shows that the difference in electronegativity between carbon and hydrogen is only 0.4
- As a result of this, alkanes are nonpolar molecules and have no partial positive or negative charges (δ+ and δ- respectively)
- Alkanes therefore do not react with polar reagents
- They have no electron-deficient areas to attract nucleophiles
- And also lack electron-rich areas to attract electrophiles
Ethane is an example of an alkane that lacks polarity due to almost similar electronegativities of the carbon and hydrogen atoms
- Due to the unreactivity of alkanes, they only react in combustion reactions and undergo substitution by halogens
Examiner Tip
Remember: nucleophiles are negatively charged and are attracted to electron-deficient regions.Electrophiles are positively charged and attracted to electron-rich regions.
