Explain the substitution reaction of a primary halogenoalkane with sodium hydroxide.

First of all, it is important to determine what kind of substitution reaction the halogenoalkane will undergo. We are given the information that it is a primary halogenoalkane, which generally undergo a SN2 reaction. 'S' standing for substituion, 'N' for nucleophilic, and '2' standing for bimolecular. The reaction is SN2 and not SN1 as the carbon centre is not sterically hindered (the nucleophile is able to 'barge' through), so attack by the nucleophile is possible. Furthermore, the transition state is more stable than the carbo-cation that would otherwise be formed.

In this particular case, the hydroxide ion attacks the carbon atom attached to the bromine in the bromoethane, as it has a partial +'ve charge, forming a high-energy transition state. The the carbon centre being bonded both to the hydroxide ion and halide ion for an intensely short period of time (imagine a weightlifter with two extremely heavy dumbells being carried by both arms). The reaction proceeds with the halide ion 'breaking off' heterolytically, the carbon-hydroxide bond being fully made, and the new subsituted product, ethanol, being formed. The second-step is the rate-determing step, thus a second-order reaction. 

Answered by Rutger S. Chemistry tutor

4411 Views

See similar Chemistry IB tutors

Related Chemistry IB answers

All answers ▸

Define and then compare the periodic table trends (atomic radius, electronegativity, ionization energy, electron affinity) for Lithium (Li) and Sodium (Na).


Explain the size of atomic radii observed in the periodic table


Why does ozone absorb a broader range of wavelengths of UV light than oxygen?


Explain the effect of increasing the temperature on the rate of reaction


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences