Chemistry · General Principles Of Organic Chemistry · NEET
A full-headed curved arrow (double-barbed, looks like a normal arrowhead) shows TWO electrons moving together as a pair. A half-headed fish-hook arrow (single barb) shows only ONE electron moving. NCERT rule: use the full arrow for heterolytic events like a nucleophile attacking an electrophile, and use the fish-hook only for homolytic cleavage that forms free radicals.
The arrow ALWAYS starts at the electron source (an electron-rich site: a lone pair, a negative charge, or a pi/sigma bond) and points TOWARD the electron-poor site (electrophile, a positive or partially positive atom). NCERT says the curved-arrow notation shows the movement of an electron pair FROM the nucleophile TO the electrophile. Never draw it from positive to negative.
It shows ELECTRONS moving, never atoms. This is the most common mistake. The tail sits on the electron pair or bond that is leaving, and the head shows where that electron pair ends up (a new bond or a lone pair). Atoms only move as a result of the electrons moving.
The tail begins exactly on the electrons you are moving. If a lone pair attacks, start the tail on that lone pair. If a bond breaks, start the tail on the middle of that bond line. Do not start the arrow on a positive charge or on an atom symbol; start it on the electrons themselves.
In homolytic cleavage the shared electron pair splits, so ONE electron goes to each atom. Since two electrons go to two different places, you need TWO fish-hook arrows, one for each single electron. A single full-headed arrow would wrongly send both electrons to the same atom, which is heterolytic (ionic), not radical.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It represents the movement of electrons from one place to another during a reaction. It is a bookkeeping tool that tracks where bonds form and break.
No. A straight reaction arrow separates reactants from products. A curved arrow is drawn inside a structure to show how specific electrons move to make the product.
Use it for the movement of an electron PAIR, such as a nucleophile donating a lone pair to an electrophile, or a bond breaking heterolytically to give ions.
Use the half-headed fish-hook arrow only for single-electron movement, which occurs in homolytic bond cleavage that produces free radicals.
NEET tests it inside mechanism questions on substitution, addition and free-radical reactions. Knowing arrow direction and type helps you predict correct products and identify intermediates like carbocations, carbanions and radicals.
