QSAR SeeQUANTITATIVE STRUCTURE-ACTIVITY RELA-
TIONSHIPS.

quantitative analysis The accurate determination of
the quantity of a substance present in a specimen.

quantitative structure-activity relationships (QSAR)
The building of structure-biological activity models by

using regression analysis with physicochemical con-

stants, indicator variables, or theoretical calculations.

The term has been extended by some authors to

include chemical reactivity, i.e., activity is regarded as

synonymous with reactivity. This extension is, however,

discouraged.

See alsoCORRELATION ANALYSIS.

quantum mechanics The fundamental physical

theory of the universe; a mathematical method of

treating particles on the basis of quantum theory,

which states that the energy of small particles is not

infinitely divisible.

quantum numbers Numbers that describe the ener-

gies of electrons in atoms; derived from quantum

mechanical treatment. Consist of primary, secondary,

azimuthal, and spin numbers.

quantum yield The number of defined events that

occur per photon absorbed by the system. The integral

quantum yield is

For a photochemical reaction,

φ= moles of reactant consumed or product

formed/moles of photons absorbed

φ= number of events

number of photons absorbed

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Q

Quantitative analysis. The accurate determination of the quantity
of a substance present in a specimen