Before you can read the parent note, you must be fluent in the tiny alphabet it speaks. Below, each symbol gets three things: plain words, the picture, and why the topic needs it. They are ordered so each one stands on the shoulders of the last.
Why the topic needs it: aldol, Claisen-Schmidt, Mannich, Perkin, Reformatsky — every named reaction in Section 3 is "enolate attacks an electrophile". One idea, six names. If a molecule has no α-H, it cannot do these — it falls back to Cannizzaro or benzoin instead. So counting α-H's is the first thing you check.
Read it top to bottom: dots and arrows let you write electron flow; electronegativity gives you the δ+ target; that target is attacked (addition) or the neighbouring H is pulled off (enolate chemistry).
What does a curly arrow's tail sit on, and where does its head point?
Tail on the moving electron pair; head on where those electrons land.
Why is the carbonyl carbon δ+?
Oxygen is more electronegative and pulls the shared electrons away, leaving carbon electron-poor.
Which half of the C=O bond breaks during nucleophilic addition — σ or π?
The weak π bond; its electrons flop onto oxygen while the σ backbone stays.
What is the difference between RCHO and R2CO?
RCHO (aldehyde) has an H on the carbonyl carbon; R2CO (ketone) has two carbon groups there.
What is a nucleophile, in charge terms?
An electron-rich species (lone pair or negative charge) that attacks electron-poor centres.
What is an alkoxide and how does it become an alcohol?
An O− carbon, formed after π electrons land on oxygen; adding H+ (workup) gives neutral –OH.
Which carbon is the α-carbon?
The carbon directly attached to the carbonyl carbon.
Why is an α-hydrogen acidic?
Removing it gives a carbanion whose charge is stabilised by delocalisation onto the carbonyl oxygen (the enolate).
What is an enolate and what does it do?
The nucleophilic species left after removing the α-H; its carbon end attacks other electrophiles (aldol etc.).
If an aldehyde has no α-H, which reactions can it still do?
Cannizzaro, benzoin, and Wittig — but not aldol-type condensations.
What does Δ over a reaction arrow mean?
Apply heat.
Recall One-line summary of the whole page
Track electron pairs (arrows) → oxygen makes carbon δ+ → nucleophiles attack that carbon, OR the acidic α-H leaves to make an enolate that attacks. Everything else is a variation. ::: This is the engine of the parent topic.
Where these foundations go next: you build alcohols by oxidising them (Alcohols — oxidation and PCC), you meet carbanion nucleophiles as Grignard reagents and organometallics, the enolate idea is the whole of Enols and enolates — keto-enol tautomerism, aryl ketones come from Friedel–Crafts acylation, and the reagents that reduce carbonyls are catalogued in Reduction reagents — DIBAL, LiAlH4, NaBH4. Carboxylic-acid products link to Carboxylic acids and derivatives.
