= Alpha-tocopherol
{title2=$\mathrm{C}_{29}\mathrm{H}_{50}\mathrm{O}_2$}
\b[Alpha-tocopherol] is the tocopherol structure with additional aromatic methyl substituents at positions 5, 7 and 8 of the <tocol> parent. ChEBI records its formula as $\mathrm{C_{29}H_{50}O_2}$ and average molar mass as approximately $430.707\,\mathrm{g\,mol^{-1}}$.<Alpha-tocopherol in ChEBI>[CHEBI:22470, Definition, Formula and Average Mass]{ref} The unqualified structural name does not identify one stereochemical configuration.
The three stereogenic positions 2, 4′ and 8′ allow eight configurations when treated as independently variable. The nomenclature recommendations designate the $(2R,4'R,8'R)$ form as <RRR-alpha-tocopherol> and distinguish <all-rac-alpha-tocopherol>, a mixture involving the stereoisomeric forms.<Nomenclature of Tocopherols and Related Compounds by IUPAC-IUB Joint Commission on Biochemical Nomenclature>[Recommendations 11–12 and Table 1]{ref} Specify stereochemistry when a particular compound or mixture is intended; “alpha” identifies the ring methylation pattern, not those three configurations.
An original counting example assumes all eight configurations occur equally. A 1 mg mixture then contains 0.125 mg of each configuration. Equal proportions are a stated hypothetical condition, not guaranteed by the word synthetic or by an unqualified analytical label. All configurations share the same molecular formula, so a measurement that reports only that formula cannot determine their proportions.
For a concentration calculation, 1.000 mg of pure alpha-tocopherol corresponds to
$$
n=\frac{0.001000}{430.707}\,\mathrm{mol}\approx2.322\,\mathrm{\mu mol}.
$$
At final solution volume 10.00 mL, the concentration is approximately $232.2\,\mathrm{\mu mol\,L^{-1}}$. Purity, volume and analyte identity enter that result. An ester derivative requires its own molar mass and reaction accounting; equal milligram amounts are not automatically equal amounts of alpha-tocopherol.
As a <radical-trapping antioxidant>, alpha-tocopherol can participate in terminating lipid-oxidation chains. A primary 1983 study compared inhibited-autoxidation estimates with <high-performance liquid chromatography> measurements of vitamin E in plasma and erythrocyte ghosts.<Is vitamin E the only lipid-soluble, chain-breaking antioxidant in human blood plasma and erythrocyte membranes? by G. W. Burton and others>[Abstract, activity/composition comparison]{ref} That is evidence linking chemical activity and composition in the studied materials, rather than a general conversion from antioxidant assay response to clinical benefit.
NIH identifies alpha-tocopherol as the form meeting human vitamin-E requirements and describes preferential hepatic handling.<Vitamin E Fact Sheet for Health Professionals by the Office of Dietary Supplements>[Introduction]{ref} Keep that biological role distinct from an analytical statement about total tocopherols, molecular amount or the stereoisomer composition of a sample.
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