Students need to know Arrow pushing in mechanisms, which I mentioned in last year’s post. This is only taught extensively in universities.
3(b)(iii) Surprisingly, this mechanism involves hemolytic fission into radicals. This question is very tough and is a great surprise. Thankfully, hints are provided. Students need to know how to draw the correct arrow hook in arrow pushing and to illustrate the dative bonds, unpaired electron(s).
(c)(ii) Students need to explain where did NO2+ come about by referring to it in the earlier parts. Students need to know their mechanisms in organic chemistry very well.
(e) Examiners favor entropy section in thermochemistry very much.
4(a) This is a great surprise as examiners seldom test on atomic structure. Students need to know what are isotopes, and alpha particles (I mentioned this last year) and the behavior of the particles in an electric field.
(c)(ii) Students also have to explain why phosphorus has a higher melting point than chlorine.
(d)(i) The question is vaguely phrased.
(e)(i) Mr Chong has seen a similar molecular structure in supramolecular chemistry (postgraduate level), eg. Crown ethers with a sodium ion in between the structure.
5(a) This part is very tricky. Students need to lengthen the carbon chain of the original molecule by 2 carbons in 2 different ways. Students need to know the conditions and reagents and of course the type of reaction to go about the synthesis.
(b)(iii) This part is very tricky. Students need to know that in K, there is hydrogen bonding to stabilize the mono-anion. Similar questions have come out in 2010-2011 papers, just that 2012 papers involves hydrogen bonding too. I have mentioned this in last year’s post.
(c) Compound L is an acid anhydride, which is out of the syllabus. I mentioned this in last year’s post. From L to M, students can speculate on the reaction.
(d) Is a little tricky. Students have to guess that from N to P, decarboxylation of the acid occurs.
As I cannot reproduce the exam papers, students need to purchase the Ten Year Series from bookshops.