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The Thermodynamics of Chemical Reactions
Published in Juan H. Vera, Grazyna Wilczek-Vera, Classical Thermodynamics of Fluid Systems, 2016
Juan H. Vera, Grazyna Wilczek-Vera
In the production of 1,3-butadiene by dehydrogenation of n-butane, it is expected to find the following chemical species: n-butane, hydrogen, 1,3-butadiene (CH2=CH−CH=CH2 or 1,3−C4H6), and the side products: 1-butene (CH2=CH−CH2−CH3 or 1−C4H8), 2-butene (CH3−CH=CH−CH3 or 2−C4H8), 1,2-butadiene (CH2=C=CH−CH3 or 1,2-C4H6), 1-butyne (CH=C−CH2−CH3 or 1−C4H6), and 2-butyne (CH3−C=C−CH3 or 2−C4H6). Determine the number of independent reactions to be considered when (1) only the above compounds are present at equilibrium and (2) N2 is added as an inert to minimize side reactions.
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.