Dear colleague,
The Royal Society of Chemistry have
recently published research which suggests a need for reconsidering explanations based on inductive effects of alkyl groups - Mark C Elliott et al, Journal of Organic and Biomolecular Chemistry, Issue 2, 2025.
The findings of this research are relevant to the following specification points of our International AS (XCH11) and International A level Chemistry (YCH11) qualifications:
- 5.6 be able to describe the mechanism (including diagrams), giving evidence where possible, of:
- the electrophilic addition of bromine and hydrogen bromide to ethene
- the electrophilic addition of hydrogen bromide to propene
Use of the curly arrow notation is expected – the curly arrows should start from either a bond or from a lone pair of electrons.
Knowledge of the relative stability of primary, secondary and tertiary carbocation intermediates is expected
- 19.3 understand that amines are miscible with water as a result of hydrogen bonding, and the reasons for the difference in basicity between ammonia, primary aliphatic amines and primary aromatic amines
The inductive effect itself is not directly mentioned in the specification. However, many textbooks have referred to it in explanations relating to the stability of cations and to the basicity of amines. Consequently, candidates have frequently referred to this effect in their examination responses and have been credited for doing so.
What does this mean for you and your learners?
In the short term, to remain compliant with wider policies and procedures, we will not be amending our specification, so we will continue to credit candidate responses as we have historically. You are not required to adapt your teaching in response to these findings.
Considering this new research, we will broaden our mark schemes to allow for alternative explanations, so as not to disadvantage particularly well-read students. We will utilise our additional guidance section of our mark schemes to ensure that no candidate is penalised for a correct answer in light of these new findings.
What about in the future?
When the specifications are reformed, we will have a chance to refresh our subject content considering new research. This will include the RSC findings into the stability of carbocations and basicity of amines.
If you have queries, please get in touch with our subject advisor, Tim Lawrence, by emailing
TeachingScience@pearson.com.
