Intuition The one core ideaEvery organic reaction is just electron pairs moving — from a place that has spare electrons to a place that wants them, breaking old bonds and making new ones. If you can count the atoms before and after and track where the electron pairs went , the four reaction types (addition, elimination, substitution, rearrangement) are simply the four possible "shapes" of that bookkeeping.
Before you can read a single arrow in the parent note, you need a toolbox. This page builds every symbol from nothing — no prior chemistry vocabulary assumed. We go in the order a reaction actually unfolds: first what a bond is , then how electrons move , then the players (nucleophile, electrophile, leaving group), then the shorthand (σ π S N 1 ∘
A tiny negatively-charged particle. Bonds are made of pairs of shared electrons . When we say "electrons move," we mean these pairs slide from one atom to another.
Definition ElectronegativityA number measuring how greedily an atom pulls shared electrons toward itself . Fluorine and oxygen are greedy (high); carbon and hydrogen are mild.
The picture: imagine two kids holding one rope (the shared electron pair). If one kid pulls harder (higher electronegativity), the rope's middle sits closer to them — that atom becomes slightly negative, the other slightly positive.
Intuition Why the topic needs thisEvery reaction in the parent note starts because one atom is electron-rich and another is electron-poor . Electronegativity is what creates that imbalance. No imbalance → no reaction.
The tiny charges are written δ + δ − + − Inductive effect for how this pull travels down a chain of atoms.
σ strong, straight bond formed when two atoms share a pair of electrons head-on, right between the two nuclei . Every single bond is a σ
π weaker, sideways bond. When atoms already joined by a σ second pair, that pair sits above and below the line joining the nuclei — not between them. A double bond = one σ π
The picture: the σ π π outside the axis, they are exposed and easy to grab.
Intuition Why the topic needs thisAddition consumes a π Elimination creates one. The whole "π bond dies / π bond born" language in the parent note is just talking about these loose sideways loops appearing or vanishing.
Definition Curved (curly) arrowA drawing symbol. A full-headed curved arrow means "this pair of electrons moves from the arrow's tail to its head ." The tail sits on the electron source (a bond or a lone pair); the head points where the new bond forms.
The picture: think of it as an instruction for the electron pair's journey , like a subway line from station A (where electrons are now) to station B (where they end up).
Intuition Why the topic needs thisEvery mechanism in the parent note — "π electrons attack H + B r − is a set of curved arrows. If you can read arrows, you can read any mechanism.
Common mistake "The arrow shows an atom moving."Why it feels right: in a hydride shift an H The fix: the curved arrow always tracks the electron pair , never the nucleus. In a "1,2-hydride shift" the arrow shows the bonding pair moving; the H
A carbon atom that has lost one bonding pair and is now short of electrons , carrying a full positive charge, written C + C + hungry for electrons.
The picture: a carbon that normally holds four ropes is now holding only three — one hand is empty and grabbing at the air. That empty, positive hand is what nucleophiles rush toward.
Intuition Why the topic needs thisThis single order is, in the parent note's words, "the 80/20 win." It decides Markovnikov (which cation forms in addition), Saytzeff (which alkene forms in elimination), S N 1 S N 2 every rearrangement. Learn it once, use it four times.
Definition Nucleophile (Nu)"Nucleus-lover." An electron-rich species that donates a pair of electrons to form a new bond. It carries a lone pair or a negative charge. Examples: O H − B r −
Definition Electrophile (E)"Electron-lover." An electron-poor species that accepts a pair of electrons. It carries a positive charge or a δ + H + δ + C–Br
The picture: the nucleophile is a magnet's north pole overflowing with electrons; the electrophile is a south pole that's starved. They snap together — electrons flow from Nu to E. See Nucleophiles and Electrophiles .
Definition Leaving group (LG)The atom/group that departs, taking the bonding pair with it , and is comfortable existing as an anion afterward. Good ones (B r − I − stable on their own. See Leaving groups .
The picture: a passenger who not only steps off the bus but keeps the shared blanket (electron pair) — and is perfectly happy standing alone on the pavement.
Intuition Why the topic needs thisSubstitution = a nucleophile pushes a leaving group off the same carbon. Addition = an electrophile then a nucleophile add across a π Elimination = a base (a nucleophile aimed at H
A formula telling how fast a reaction runs and what it depends on . Rate = k [ X ] X [ ]
Rate = k [ substrate ] only the substrate matters in the slow step (one molecule in the bottleneck). This is the "1" in S N 1 E 1 Rate = k [ substrate ] [ Nu ] two molecules meet in the slow step. This is the "2" in S N 2 E 2
Intuition Why the topic needs thisThe subscript number in S N 1 S N 2 E 1 E 2 how many species show up in the rate-determining step — see SN1 vs SN2 mechanisms and E1 vs E2 mechanisms . It is not a random label.
Definition Decoding the labels
S S ubstitution.N N ucleophilic → a nucleophile does the attacking. So S N E S E lectrophilic → S E Aromatic Electrophilic Substitution ).Standalone E E limination.
The trailing 1 2
S N 2 S ubstitution, N ucleophilic, 2 molecules in the slow step." Every symbol earns its place.
Definition Degree of unsaturationA count of how many rings + π a molecule has. Each double bond = 1, each ring = 1. It tells you "how far from fully-saturated (all single bonds) am I?"
Electronegativity - unequal pull
Partial charges d+ and d-
Nucleophile Electrophile Leaving group
Curved arrow - electron pair moves
Carbocation and stability
Rate law - k times concentrations
Types of organic reactions 4.1.11
This map shows the build order: greediness of atoms creates charges → charges define the players → arrows move their electrons → the carbocation is the pivot that everything (rate, labels) depends on → the parent topic sits on top.
What does electronegativity measure? How greedily an atom pulls a shared electron pair toward itself.
What do δ + δ − Slightly positive / slightly negative partial charges from unequal electron sharing.
Where do the electrons of a π Above and below the internuclear axis, exposed — so they are weak and easy for electrophiles to attack.
Which is weaker, a σ π The π
What does a full-headed curved arrow represent? The movement of one electron pair from tail (source) to head (new bond), never an atom.
What is a carbocation and what is its stability order? A carbon short one bonding pair, carrying + 3 ∘ > 2 ∘ > 1 ∘ > methyl
Define nucleophile and electrophile in terms of electrons. Nucleophile = electron-rich, donates a pair; electrophile = electron-poor, accepts a pair.
What makes a good leaving group? One that departs with the bonding pair and is stable as an anion (e.g. B r − I −
What does the subscript number in S N 1 E 2 The number of species in the rate-determining (slow) step.
How does degree of unsaturation change for addition vs elimination? Drops by 1 for addition, rises by 1 for elimination, unchanged for substitution and rearrangement.
