The ideas behind the reactions
One question per page, answered in the first two sentences and then earned. Each one ends where the idea can be watched happening — a mechanism on your own structures, a molecule with its measured properties, a calculator that shows its working.
Concepts
What is the difference between SN1 and SN2?
Both replace a leaving group with a nucleophile, and they differ in whether the bond breaks before the new one forms. SN2 does it in one motion and turns the carbon inside out; SN1 lets the leaving group go first, makes a carbocation, and whatever attacks it can attack from either face.
What is a leaving group, and why are some better than others?
A leaving group is whatever leaves taking the bonding electrons with it. How good it is comes down to one question: how comfortable is it holding that negative charge once it has gone?
What is the difference between a nucleophile and an electrophile?
A nucleophile has electrons to give and an electrophile has somewhere to put them. Every curly arrow in every mechanism runs from the first to the second, which is why getting this right makes mechanisms readable rather than memorised.
What is Markovnikov's rule?
Adding HX across an alkene puts the hydrogen on the carbon that already has more of them, and the X on the other. The memorable phrasing hides the actual reason, which is that the reaction goes through whichever carbocation is more stable.
What is a functional group?
A functional group is an arrangement of atoms that behaves roughly the same way wherever it appears. It is why a chemist can look at an unfamiliar molecule with an ester in it and already know several things it will do.
What do the curly arrows in a mechanism actually mean?
Each curly arrow means one pair of electrons moved: the tail sits where the pair is now, the head where it goes. Nothing else about the drawing is arbitrary, which is why a mechanism can be checked rather than memorised.
What these are not
They are not a course, and they are not a replacement for one. Each page exists because it is a question people actually ask, and it tries to answer that question properly rather than to cover a syllabus.
Where an idea has exceptions, the page says so on the page rather than in a footnote — a concept page is where a misconception gets installed, and the tidy version is usually the one that stops working first. Where the platform can show the idea rather than describe it, the page hands you over to the mechanisms or prediction, which is the part a textbook cannot do.