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Organic Chemistry Nomenclature
Published in Arthur W. Hounslow, Water Quality Data, 2018
Hydrocarbons are named by assigning a prefix that indicates the number of carbon atoms in the chain and a suffix indicating the degree of unsaturation. If saturated, that is, the compound contains only single bonds, then the ending is -ane. Examples are methane, ethane, propane, butane, and pentane, each designating saturated hydrocarbons with one, two, three, four, and five carbon atoms, respectively. A more comprehensive listing is given in Table 7.2. Compounds with double or triple bonds have endings -ene or -yne, respectively. A two-carbon compound with one double bond is ethene (old name ethylene). A three-carbon compound with one triple bond is propyne.
High-resolution photoelectron spectrum of the origin band of the X̃+ 2E ← X̃ 1A1 ionising transition of propyne
Published in Molecular Physics, 2018
Propyne (H–CC–CH3) and its cation play an important role as intermediates in combustion processes [1] and astrochemistry [2,3]. The ground electronic state of H–CC–CH+3 is formed upon removal of an electron out of the doubly degenerate outer-valence-shell molecular orbital (e symmetry, C≡C-triple-bond π character) of propyne. Therefore, the propyne radical cation has a doubly degenerate ground electronic state (2E in the C3v(MS) group), which implies the simultaneous occurrence of the Jahn–Teller (JT) effect and spin-orbit coupling, as in the case of the radical cation of 2-butyne [4]. The highest occupied molecular orbital (HOMO) of propyne resembles that of acetylene and 2-butyne, and the electron-hole probability density is mainly located on the CC triple bond. In the case of acetylene, the molecular cation is linear, and the Renner–Teller effect does not significantly affect the ground vibronic state, which is split into two spin-orbit components separated by Aso+ = −30.86(44) cm−1 [5], where the negative sign indicates an inverted order with the 2Π3/2 component lying below the 2Π1/2 component. In the case of 2-butyne, the equilibrium structure of the cation is slightly distorted by the JT effect, which reduces the spin-orbit splitting to a value of Aso+ = −10.5(10) cm−1 [4]. A similar reduction of the spin-orbit splitting is also expected in the ground-state of the radical cation of propyne [6] and was indeed observed [7,8], as discussed below.