The Functional Groups
This is where weaponised innuendo and humour are in the name of memory and study.
Each functional group has some gloriously unhinged description designed to lodge itself in your brain. If you hear these lines in your head during an exam, that’s your cue to thank (or blame) me; my take on them is meant to be seared into your memory.
Hydrocarbons: The Naked Basics (Just C and H)
Hydrocarbons are the simplest molecules in organic chemistry, just carbon and hydrogen, no oxygen, no nitrogen, no drama. They’re the backbone that everything else gets bolted onto.
In herbal chemistry, whole families of constituents (especially terpenes and essential oil components) are built from hydrocarbon skeletons, often with a few extra functional groups added later to spice things up.
Alkanes - vanilla, all single bonds
Alkenes - double-bond divas
Alkynes - triple-bond intensity
Arenes - aromatic rings (think benzene and friends)
Simple Oxygen Heteroatomic: Oxygen Sticks Its Oar In
Once oxygen turns up, carbon chains stop quietly minding their own business and start interacting with everything. These are your pre-carbonyl oxygen groups – no C=O yet, just oxygen sticking its nose in and changing solubility, boiling point and general drama levels.
Meet the alcohols at The O–H Arms – O–H hanging off the end of the chain, getting very involved with hydrogen bonding. Next door, we’ve got the ethers, where oxygen sits sensibly in the middle as C–O–C, acting like a bridge between two carbons and pretending not to be polar. And then there are the epoxides: tiny three-membered C–O–C rings under far too much strain, predictably reactive, like someone who’s had no sleep and three espressos.
This section covers:
Alcohols (–OH) – the clingy ones.
Ethers (C–O–C) – oxygen playing bridge between two carbons.
Epoxides (are 3-membered C–O–C rings, stop laughing) – small, stressed and very reactive.
Carbonyl Compounds: C=O and a Sense of Importance
Add a carbonyl group (C=O), and suddenly the molecule thinks it’s special. Electrons shift, polarity changes, reactions start happening, and now we all have to pay attention.
Aldehydes (–CHO) – carbonyls lurking at the end of the chain, ready to react with almost anything that makes eye contact.
Ketones (>C=O) – carbonyls in the middle, annoyingly stable but still quite happy to get involved in reactions when it suits them.
Carboxylic acids (–COOH) – permanently slightly offended and always ready to donate a proton about it.
Esters (–COOR) – smell lovely, pretend to be harmless, quietly hydrolyse behind your back.
Amides (–CONH–) – carbonyls that have settled down with nitrogen and are now very sensible about their reactivity.
Nitrogen-Based Groups: The Ones That Get Involved in Everything
Add a carbonyl group (C=O), and suddenly the molecule thinks it’s special. Electrons shift, polarity changes, reactions start happening, and now we all have to pay attention.
Aldehydes (–CHO) – carbonyls lurking at the end of the chain, ready to react with almost anything that makes eye contact.
Ketones (>C=O) – carbonyls in the middle, annoyingly stable but still quite happy to get involved in reactions when it suits them.
Carboxylic acids (–COOH) – permanently slightly offended and always ready to donate a proton about it.
Esters (–COOR) – smell lovely, pretend to be harmless, quietly hydrolyse behind your back.
Amides (–CONH–) – carbonyls that have settled down with nitrogen and are now very sensible about their reactivity.
Sulphur-Based Groups: You’ll Smell These Before You See Them
Sulphur doesn’t appear everywhere, but when it does, it has main character energy and isn’t subtle about it. These groups are behind many of the “good for you, terrible for your social life” plant smells, think garlic, onions, brassicas and that one person who brings boiled eggs to work.
Thiols (–SH) – alcohols’ feral cousin: lives in garlic and onions, refuses deodorant.
Thioethers/sulphides (C–S–C) – sulphur quietly sitting where oxygen might have been, but with far stronger opinions about odour.
Disulfides (–S–S–) – sulphur-sulphur handshakes that help proteins keep their shape and your kitchen smell like you mean business.
Aromatic: Rings, Resonance and Showing off
Aromatic rings are chemistry’s answer to people who are both clever and good-looking. Benzene and friends are unusually stable, annoyingly useful, and everywhere in plant chemistry.
Arenes (benzene rings/aryl groups) - six carbons, delocalised electrons, and a tendency to turn up in anything interesting.
Phenyl groups (–C₆H₅) - benzene rings used as decorative attachments on larger molecules.
Phenols (aromatic –OH) - benzene plus –OH: often colourful, often antioxidant, occasionally a bit aggressive.