Intuition The ONE core ideaAn amine is nitrogen carrying a lone pair — two electrons that belong to no bond and sit ready to be given away. Everything in this whole topic (basicity, Hofmann, carbylamine, Hinsberg) is just one question repeated: how available is that lone pair, and what does it attack?
Before you can follow a single line of the parent note, you need to actually see what a lone pair is, what R p K b
A lone pair is a pair of electrons on an atom that is not shared in any bond. Nitrogen in an amine has exactly one such pair.
Nitrogen has 5 electrons in its outer shell. In ammonia (N H 3 three of them to bond to three hydrogens. That leaves two electrons with no job — they huddle together as a pair, pointing off into empty space above the nitrogen.
Intuition Why we care so much about this pairA bonding pair is "spoken for" — it is glued between two atoms. The lone pair is free . It is the only pair the nitrogen can offer to something else: to a proton (making the amine a base) or to a hungry carbon (making it a nucleophile). The entire topic is the biography of this one pair.
The picture also shows the shape: the three N–H bonds plus the lone pair push apart into a pyramid . The lone pair takes up the fourth corner.
R R any carbon-based group hanging off the nitrogen — a methyl C H 3 C H 3 C H 2 R pattern without committing to one specific molecule.
So the parent's R - N H 2
The number of N–H bonds left is the hero number of this whole topic. It decides the carbylamine test (needs two N–H), the Hinsberg test (needs at least one N–H), and how well a protonated amine is solvated. Keep counting them.
1° has 2 N–H, 2° has 1 , 3° has 0 . Every time you add an R delete an H . "More carbon in, less hydrogen left."
N ¨ N ¨ are the lone pair drawn explicitly. When you see : C C l 2 that carbon also carries a lone pair (it too is hungry to bond).
Definition The curved arrowA curved arrow in chemistry means "a pair of electrons moves from the tail to the head ." It always starts at a lone pair (or a bond) and points to where those electrons are going. It is the verb of chemistry — it tells you the action .
Intuition Nucleophile vs electrophile — who gives, who takes
A nucleophile is "nucleus-loving": it is electron-rich and offers its pair. An amine, with its free lone pair, is a nucleophile.
An electrophile is "electron-loving": it is electron-poor and wants a pair. A proton H + C 6 H 5 S O 2 C l : C C l 2
Every reaction in the parent note is one arrow: the amine's lone pair (nucleophile) reaching toward an electrophile. Grabbing H +
A base donates a lone pair to a proton H + is the definition of a base in action:
R - N H 2 + H 2 O ⇌ R - N H 3 + + O H −
Read the pieces:
H 2 O acid (supplies the H + The half-arrows ⇌ both ways and settles at a balance point (equilibrium).
R - N H 3 + after grabbing the proton — now positively charged. This is called the conjugate acid .O H −
K b p K b K b how far right the equilibrium sits — a big K b R - N H 3 + O H − strong base .
Because K b 1 0 − 4 1 0 − 10 p K b = − log 10 K b
The log ruler-shrinker . The minus sign flips the direction, so:
Why smaller? Big K b p K b small . So aniline's p K b ≈ 9.4 weak base, while a methylamine's p K b ≈ 3.4 strong one.
Common mistake Steel-man: "Bigger number means stronger, surely?"Why it feels right: for most measurements, bigger = more. The flaw: p K b negative log, so it runs backwards. Fix: picture the number line — strong bases live on the left (small p K b
These three words appear all over the parent note. Each is just a reason the lone pair becomes more or less available.
Definition Inductive effect (+ I pushes electron density along the bond toward the nitrogen. The + I H + Resonance & Inductive Effects .
Definition Resonance (delocalisation)Sometimes a lone pair can spread out into a neighbouring ring or double bond, smearing itself over several atoms. When aniline's lone pair leaks into the benzene ring, it is busy and no longer free to grab a proton — so aniline is a weak base. See Resonance & Inductive Effects .
Water molecules cluster around a charged particle and stabilise it with hydrogen bonds. A protonated amine R - N H 3 + more handles for water to grab, so it is more stabilised. Fewer N–H bonds (like tertiary R 3 N H + Solvation and Hydrogen Bonding and Acid–Base Theory & pKa/pKb .
Intuition The tug-of-war in one sentenceIn water , basicity = (how much + I gas phase there is no water, so the solvation term vanishes and only + I
≡ R - N ≡ C triple bond : three shared electron pairs between the N and C. It is what makes isocyanides such strange, foul-smelling molecules.
β α next carbon over is β β β β α β E2 Elimination & Zaitsev vs Hofmann Orientation .
Amine acts as nucleophile
Beta hydrogen and leaving group
Cover the right side and test yourself — you are ready for the parent note when every line is instant.
What is a lone pair, in one phrase? Two electrons on an atom not shared in any bond — nitrogen's free, giveable pair.
What does the symbol R Any carbon-based group (methyl, ethyl, phenyl, …) attached to the nitrogen.
How many N–H bonds does a 1°, 2°, 3° amine have? 1° has 2, 2° has 1, 3° has 0.
What does a curved arrow mean? A pair of electrons moves from the arrow's tail to its head.
Nucleophile vs electrophile? Nucleophile is electron-rich and gives a pair; electrophile is electron-poor and wants one.
What does N ¨ The nitrogen's lone pair drawn as two dots.
In R - N H 2 + H 2 O ⇌ R - N H 3 + + O H − R - N H 3 +
Does smaller or larger p K b Smaller p K b
What does + I Pushes electron density onto nitrogen, enriching the lone pair so it grabs H +
Why does resonance weaken aniline's basicity? The lone pair spreads into the benzene ring and is no longer free to grab a proton.
What does solvation do to a protonated amine? Water H-bonds to its N–H bonds and stabilises the cation — more N–H means more stabilisation.
What is a β A hydrogen on the carbon one bond away from the carbon bearing the leaving group.
Linked foundations: Resonance & Inductive Effects · Solvation and Hydrogen Bonding · Acid–Base Theory & pKa/pKb · E2 Elimination & Zaitsev vs Hofmann Orientation · Diazonium Salts & Aniline Reactions · Amines — Preparation (Gabriel, reduction, Hofmann bromamide) · back to the parent topic
