Chemistry B

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Lectures

Chemistry B is one of the more popular subject choices in Part IB, with cohort sizes usually of around 150 students. It is usually taken by those also taking biological subjects who wish to gain a more ‘chemical/molecular’ perspective in these subjects. Chemistry B spans organic, inorganic, and biological chemistry, leading up smoothly from Part IA Chemistry and further laying the foundation for further, more specialized topics to come in Part II in (in)organic and biological chemistry. Courses are still focused on an introductory aspect, with many new foundational concepts introduced for the first time. As a standard, most lecturers prefer to leave blanks in the notes for annotation during lectures. As usual, going quickly through the notes ahead of the lectures will undoubtedly help in one’s understanding of the subject during the lecture. Lectures are usually at 9am on Tuesdays, Thursdays, Saturdays, unless informed otherwise. Students will be lectured by an excellent entourage of experienced chemists, all of which are more than happy to take questions in their respective areas of expertise.

The lecture course is overall well-structured, with each term corresponding to a specific area of chemistry. A brief description of each lecture series is explained as below:

Michaelmas (Organic):

  • Aromatic and Enolate Chemistry: The first part of the course covers the reactions that aromatic rings undergo, with an emphasis on substitutive regioselectivity. The second part then moves on to explore enolate formation, stabilization, and reactions, which are extremely useful species for the synthetic chemist.
  • Nucleophilic Attack on π Systems: Explains the ins and outs of conjugate addition (Michael addition), including selectivity (vs direct addition), as well as the ever-so important nucleophilic aromatic substitution reaction. There is also a brief explanation of chirality here, using the Cahn-Ingold-Prelog (CIP) rules.
  • Introduction to Stereochemistry: Chirality is explained in further detail here, as well as different ways of visualizing molecules in 3D. The importance of the spatial configuration of molecules is highly emphasised, as illustrated by differences in reaction rates and spectroscopic data. There will be a great deal of ring visualization, as explained via a variety of cyclisation reactions.
  • Shape and Organic Reactivity: This lecture course focusses mainly on covering various important organic reactions which are highly useful in synthetic chemistry. Some reactions may have been explained before in Part IA, while others are completely new. The course covers alkene, alkyne and carbonyl chemistry, with new reactions such as ozonolysis, oxymercuration and Beckmann rearrangements. Stereoselectivity via the Felkin-Anh model and Houk’s rule will also be explained in detail.

Lent (Inorganic):

  • Transition Metal (TM) Chemistry – Structure, Bonding and Reactivity: Get ready, because this lecture course comprises of 17 lectures, split into two parts. The first part covers the basics of TM chemistry, explaining ligand types via molecular orbital (MO) theory and ligand crystal field theory (CFT). These can be used to further explain physical properties of complexes and justify ligand/metal positions in their respective Spectrochemical Series.After laying the foundation, the reactivities of TM complexes are discussed in greater detail in the second part. Important concepts include hard-soft acid-base (HSAB) theory and the all-important electron counting techniques. Ligand properties are further explained, in conjunction with key reactions in catalysis involving TM complexes. This part of the course will cover a huge amount of content, and it is highly advised to minimally stay on par with the lectures here.
  • Structure, Bonding, and the p-Block elements: A slight detour into main group chemistry, this course will cover the chemistry behind numerous p-Block elements. Starting off with a brief insight into the theory behind the formation of hypervalent compounds, the course proceeds into the chemistry behind O containing rings/chains (e.g. P=O, Si-O etc.). Next is a key highlight of this course, which involves learning the chemistry behind B/N, P/N and S/N rings and how we can compare them in terms of their structure and bonding. The course then rounds off with a touch on multinuclear NMR spectroscopy and a hint of EPR spectroscopy. Beware, ALL parts of this course are examinable – however esoteric they may appear to be.

Easter (Biological):

  • Introduction to Chemical Biology: The final lecture course of 11 lectures provides a more “chemical” approach to common biological topics and concepts. Those who have taken biological subjects covering some aspect of molecular biology will have had some background knowledge in this course, which is split into 2 parts. The first part covers a recap of non-covalent interactions, and a more molecular view of nucleic acid and protein structure. A key examinable component of this part is the ability to design a small molecule able to bind well to the pocket of a receptor via maximizing intermolecular interactions. The second part of this course will cover different methods of biological catalysis with a variety of enzymes as examples. It ends off with a brief explanation of how enzyme inhibitors are designed. Examinable components involve identifying possible catalytic mechanisms based on various experimental data provided (e.g. Kinetic Isotope Effect [KIE], site directed mutagenesis etc.).

Supervisions

As usual, each lecture course comes with a variety of fun and engaging supervision questions to assist you in navigating the ins and outs of each course. In particular, the 1st lecture course will have many more questions than what is required for the usual supervision, which are great for additional practise. Do note that some questions are a little funkier than others and may not be fully representative of the types of questions that may be examined, but instead assist in the student’s appreciation of the topics involved – so don’t take these too seriously. (However generally of course, it is important, to take your work seriously!) Often, supervisors are willing to discuss the written answers to the supervision questions (which importantly, may not even be entirely correct!). As always, come prepared having revised on the topic to be discussed for a fruitful session!

Practicals

As opposed to Part IA, Part IB Chemistry B features a chemistry practical every week in the afternoons. The main difference is that practical hours are mainly allocated for only lab work. The lab write-ups (reports) will be written entirely (and formatted) on your own outside of practical hours. You’ll have a week after each practical to complete the write-up, during which you’ll have the opportunity to come to the lab in the morning for analytical work, which mainly encompasses taking the IR spectra, melting point, and TLC, and any other relevant characteristics measurements of your compound (where applicable). The analytical results will have to be attached to your final lab report to be submitted.

The lab report is marked out of 10, with marks allocated for appropriately completed sections such as reaction mechanisms, experimental protocol, accurate spectra assignment and analysis, your calculations, and lastly any relevant theory questions in the lab booklet for that practical. Marking varies vastly across different lab demonstrators, though marks will be moderated accordingly for each demonstrator. It is crucial to ask your demonstrators if you are unsure of what is required in the lab report, or if you’re having trouble with the experiment. One top tip is to always clarify the purpose of each step of the protocol (e.g. purpose of adding 10 ml of reagent X), which will both help you in writing the lab report, and having a greater appreciation for experimental chemistry.

E.g. Your practical session is on Thursday afternoons. You spend the whole Thursday afternoon happily mixing chemicals and when you’re done, you place your product in the desiccator before leaving. You then come back on Friday/Monday/Tuesday/Wednesday morning (of your own choice) to complete your analysis of your product before compiling and submitting your report on the following Thursday afternoon before you start your next practical.

Revision and Exams

Past papers are once again (no surprise) your best friend for revision. Though the format may vary slightly over the years, the overall segregation of questions corresponds to each lecture course rather consistently. These provide the best practice for what may come up in an exam, because as you have guessed, they have come up in the exams before! With close to 25 years of past papers, you’ll have more than enough resources to hone your skills in Tripos-style questions. As luck would have it, chemists have been blessed with suggested answers that have been provided by faculty members, with a large emphasis on “suggested”. These are ever so useful to cross-check your answers with and gauge the standard of answers that examiners will be expecting. As always, there is more than one answer to a question and should you have an alternative way to approach the question, it would be a good idea to bring it up for discussion with your supervisor.

Chemistry B culminates in two 3-hour-long papers, which are very non-confusingly named Paper 1 and Paper 2, each with 5 compulsory questions. In recent years, Paper 1 tests both organic and biological chemistry, drawing on content from the whole of Michaelmas term and half of Easter term. There will be 1 question centred on each of the four organic courses, and 1 question on either half of the chemical biology course. Paper 2 tests inorganic and biological chemistry, drawing on content from the whole of Lent term and the other half of Easter term. Generally, there will be 1 question from each half of the TM course, and 1 question that is a mix of both halves. There will also be 1 question from the P-block element course, and the last question from the remaining half of the chemical biology course.

Time is of the essence in these papers, with an average of 36 minutes for each question. As such, timed practise is crucial leading up to the exams. As the old saying goes, if you must stop to ponder, your marks are miles yonder. Though also importantly, focus on completion, not perfection. A paper with fully and decently attempted questions will usually gain more marks than completing 60% of the paper “perfectly” and then not-so-gracefully running out of time.

N.B.: Do note that the format of papers has changed in 2012 from choosing 5 questions from 7 to answering all 5 compulsory questions for each paper – meaning more questions to practise! Also, there is an erratum in 2005 Paper 1 Q3bi and 2017 Paper 1 Q4b (yes, they are the same question, questions do get reused!) – the sulfone in compound C will remain a sulfone when converted to compound D.

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