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An anion formed by removing the terminal proton of an alkyne, $\mathrm{RC}\equiv {\mathrm{C}}^{-}$. It can act as a carbon nucleophile, for example in addition to a ketone.

The conjugated aldehyde $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHCHO}$. A carbon nucleophile can add at its carbonyl carbon or, in a conjugate addition, at the terminal beta carbon. Atom mapping distinguishes the two products.

An acyl chloride contains $\mathrm{R}-\mathrm{C}(\mathrm{O})\mathrm{Cl}$. Addition of a nucleophile and chloride elimination is a common substitution pathway.

An aspartic protease is a protease whose catalytic chemistry depends on aspartic acid side chains. In common examples, their carboxyl groups position and activate a water molecule for peptide bond hydrolysis. Water supplies the attacking nucleophile, unlike a mechanism in which an enzyme side chain itself makes the initial covalent attack.^[ref]

The name concerns catalytic groups, rather than requiring an aspartic-acid residue at every substrate cleavage site. Substrate recognition and catalytic mechanism are distinct properties.

HIV-1 protease provides an experimentally characterized example. In 1989, T. D. Meek and colleagues measured apparent masses of approximately 11,000 under denaturing conditions and 22,000 under nondenaturing conditions; protein cross-linking supplied additional evidence for an active protein dimer. The ratio $22,000/11,000=2$ explains the subunit interpretation.^[ref]

The same study found pH-dependent inactivation consistent with a required unprotonated carboxyl group in the active site. Combining this chemical perturbation with cleavage activity and subunit measurements supported a catalytic classification more specifically than the enzyme's molecular mass alone.^[ref]

Conjugate addition of a nitrogen nucleophile to an electron-poor alkene. Intramolecular addition can close a nitrogen-containing ring.

Base-promoted bimolecular acyl substitution: nucleophile addition gives a tetrahedral intermediate, then a leaving group departs from the acyl carbon.

Approach of a nucleophile opposite the leaving-group bond permits bond formation with inversion at the attacked tetrahedral carbon in an SN2 pathway.

Benzaldehyde is ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CHO}$, an aldehyde whose carbonyl carbon is attached directly to a phenyl group. It combines aromatic-ring chemistry with reactions of an aldehyde carbonyl.

Addition of an appropriate nucleophile at the carbonyl carbon gives a new tetrahedral centre. Because benzaldehyde has no ordinary enolizable alpha carbon, its role in an aldol reaction commonly differs from that of an enolate-forming partner.

Benzoyl chloride is the aromatic acyl chloride ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}(=\mathrm{O})\mathrm{Cl}$. Its acyl carbon is susceptible to attack by a nucleophile, followed by chloride departure.

Reaction with an alcohol can give a benzoate ester, while an appropriate amine can give a benzamide. The common acyl-substitution pattern connects these two classes of product.

Borazine dearomatization interrupts the planar pi system, for example when a nucleophile makes one boron tetrahedral. In a metal pi complex, this can change ring hapticity and produce a charged ligand with a different donor count.

Addition of bromine and an oxygen nucleophile across an alkene to form a bromoether. Intramolecular attack on a bromonium ion can close a ring; tether length, charge distribution and anti opening determine the resulting connectivity.

The Bürgi-Dunitz trajectory describes the preferred approach of a nucleophile toward a carbonyl carbon, usually at an obtuse angle to the carbon-oxygen bond, often near $107^{\circ }$. It is a geometrical trend, not a fixed angle obeyed by every reacting system.

An oblique approach balances favorable interaction with the carbonyl antibonding orbital against repulsion from occupied orbitals. Crystallographic observations of close contacts motivated this picture, linking static molecular structures with a possible path of nucleophilic addition. Steric constraints and the other substituents can modify the accessible trajectory.

Caroline Walford coauthored research on thiophenol.^[ref]

Thiophenol is $\mathrm{PhSH}$. Its conjugate base is thiophenolate, $\mathrm{Ph}{\mathrm{S}}^{-}$, a sulfur-centered nucleophile.

Oppositely charged ions remaining in direct contact without an intervening complete solvent shell. Their relative positions can bias substitution stereochemistry even when bond cleavage precedes nucleophile attack.

$\mathrm{C}{\mathrm{N}}^{-}$. Its carbon end can act as a nucleophile toward an alkyl leaving group to form a nitrile with one additional carbon.

Desilylation removes a silyl group. Attack by a nucleophile at silicon can pass through a pentacoordinate silicon arrangement before Si–O cleavage; the liberated oxygen may be trapped by a new electrophile.

Diisopropylethylamine is a sterically hindered tertiary amine base. It can remove protons and trap acid while competing relatively weakly as a nucleophile.

An electrophile accepts an electron pair in forming a bond. Reaction selectivity depends on both the electrophile and its interacting nucleophile.

The susceptibility of a species or atomic site to accepting an electron pair from a nucleophile. It depends on structure, charge and reaction conditions.

Enamine alkylation forms a carbon–carbon chemical bond by using an enamine as a carbon-centred nucleophile. The nitrogen substituent donates electron density into the adjacent carbon–carbon double bond, enabling attack on an appropriate alkyl electrophile.

In the familiar carbonyl-functionalization sequence, a ketone or aldehyde first forms an enamine with an amine. Carbon alkylation gives an iminium-containing intermediate, and hydrolysis restores the carbonyl group. The net result can be substitution next to the original carbonyl carbon. Regioselectivity, competing nitrogen alkylation and substrate compatibility matter; the net product formula does not specify a universally selective reaction.