THF: Abbreviation of tetra-hydro-furan (see Furan), a common solvent in organic reactions.

TMS: Abbreviation of tri-methyl-silane (-SiMe3).

Tautomerism: Some functional groups are related to other functional groups by a simple H shift – they are tautomers, and conversion between them is called tautomerism. The main example of this is keto-enol tautomerism.

Template Effect: Complexation of a ligand to a metal ion stabilizes one component of a mixture, shifting the equilibrium in that mixture in favour of production of the metal complex.

Term Symbols: This is a way of describing the spin, orbital, and total angular momentum of a species.

Tertiary: See also secondary. A carbon centre described as tertiary has one functional group and three other carbons attached to it. A nitrogen centre is tertiary if it has three carbons bonded to it.

Thermal energy, kT: The energy available from the thermal motion of particles at a particular temperature.

Thermal motion: The oscillation of particles about a mean position that occurs when they possess energy.

Thermodynamic Control: A reaction under thermodynamic control will produce, in the greatest proportion the most stable possible product.

Thermodynamic Product: If multiple products are possible in a reaction, the thermodynamic product is the most stable of those. Will be formed if the reaction is under thermodynamic control. See also kinetic product.

Torque: The rotational analogue of force, being given by the force multiplied by its perpendicular distance from the axis of rotation.

Transition Frequency: For a given transition with energy gap ΔE between the two states, the frequency such that ΔE = hν.

Transition State: A state during a reaction that the reactants may pass through – a high energy state that will not be isolated. Compare with intermediate.

Trans: Two substituents that are trans to each other are on opposite sides of a bond.

Trigonal Bipyramid: A five-coordinate polyhedron.

Trigonal Planar: A flat triangle shape;

Triple point: A point at which three phase boundaries meet. It is most commonly applied to the point at which solid, liquid and vapour phases simultaneously coexist. It is a characteristic of a particular substance.

Triplet States: This is a state which has two electrons with parallel spins.

Tumbling: See Molecular tumbling.

Tunnelling: Penetration of particles into areas of potential that classically they would be forbidden to enter.