= trans-Stilbene
<trans-Stilbene> is the E geometric isomer of 1,2-diphenylethene: two <phenyl groups> attach to opposite carbons of a central carbon–carbon <double bond>, on opposite sides of that double bond. Its <molecular formula> is $\mathrm{C_{14}H_{12}}$, and its CAS identifier is103-30-0.<trans-Stilbene in the NIST Chemistry WebBook>[CAS identifier, E-isomer structure and formula; linked PubChem CID638088.]{ref}
The formula can be counted directly from $\mathrm{C_6H_5-CH=CH-C_6H_5}$: two phenyl groups contribute twelve carbons and ten hydrogens, and the central pair contributes two carbons and two hydrogens. <cis-Stilbene> has the same atom counts but a different arrangement around the double bond. <Cis-trans isomerism> therefore concerns structure, not a difference in <molar mass> or elemental composition.
This makes a useful distinction in spectroscopy: a molecular formula alone does not specify every vibrational feature or optical response. Structural assignments require appropriate comparison data and a stated sample environment. In an original mixture example, equal amounts of cis and trans material still have the same total carbon-to-hydrogen ratio as either pure isomer; elemental composition alone cannot reveal that mixture.
A primary subsurface <Raman spectroscopy> experiment used trans-stilbene powder beneath a1-mm layer of <poly(methyl methacrylate)> powder. Collecting scattered light from regions laterally displaced from the excitation spot improved the unprocessed contrast of the buried trans-stilbene layer by a reported factor19.<Subsurface Probing in Diffusely Scattering Media Using Spatially Offset Raman Spectroscopy by P. Matousek and others>[Abstract, physical feasibility sample and contrast improvement.]{ref} The compound served as a chemically identifiable buried layer, illustrating how collection geometry can change which material dominates a measured spectrum. That reported contrast gain is a property of the experiment, not a universal material constant of trans-stilbene.
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