Tag: Synthesis

Organic Chemistry · Aromatic Diazonium Salts: The Most Versatile Intermediate in Aromatic Chemistry One functional group that can be replaced by almost anything, which makes it the standard route to substituents that cannot be installed directly. BSc & MSc · Organic Chemistry · Method The short answer: An aromatic amine treated with nitrous acid at low temperature gives a diazonium salt. Nitrogen is an outstanding leaving group, so the diazonium group can be replaced by halide, hydroxyl, cyano, hydrogen and more — giving access to substitution patterns unreachable by direct electrophilic substitution. Preparation An aromatic primary amine is treated with…

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Organic Chemistry · Synthesis The Wittig Reaction: Making Alkenes Where You Want Them Its value is not that it makes alkenes but that it puts the double bond in an unambiguous position, which elimination cannot guarantee. BSc & MSc · Organic Chemistry · Method The short answer: A phosphorus ylide adds to a carbonyl, and the resulting four-membered intermediate collapses to give an alkene and a phosphine oxide. The double bond forms exactly where the carbonyl was, with no possibility of migration — which is what makes it superior to elimination for regiochemical control. Why it matters Elimination reactions make…

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Organic Chemistry · Synthesis Retrosynthetic Analysis: Thinking Backwards From the Target Synthesis questions become tractable when you stop asking what the starting material can do and start asking what the product could have come from. BSc & MSc · Organic Chemistry · Method The short answer: Work backwards from the target, breaking bonds at strategic points to give simpler precursors. Each disconnection must correspond to a real forward reaction. Identifying which bond to break comes from recognising the functional group relationships that known reactions produce. The basic move A disconnection is a bond broken on paper, in the reverse direction…

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Organic Chemistry · Synthesis Protecting Groups: When to Use One and How to Choose A synthesis question that looks impossible usually becomes routine once you notice which group needs protecting. BSc & MSc · Organic Chemistry · Method The short answer: A protecting group temporarily converts a reactive functional group into an unreactive one so a reaction can be performed elsewhere. It must go on selectively, survive the intended reaction, and come off under conditions the rest of the molecule tolerates. Failing any of those three makes it useless. The problem being solved Most reagents are not perfectly selective. A…

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