The Guinness Molecules for the Carbohydrate Formula

Abstract

A systematic review and analysis of the most stable spatial arrangements of n carbon, n oxygen, and 2n hydrogen atoms including vibrational zero-point energy up to n = 5 shows that small-molecule aggregates win, typically followed by thermally unstable molecules, before kinetically stable molecules and finally carbohydrates are found. Near n ≈ 60 a crossover to carbon allotropes and ice as the global minimum structure is expected and the asymptotic limit is most likely graphite and ice. Implications for astrochemical and fermentation processes are discussed. Density functionals like B3LYPD3 are found to describe these energy sequences quite poorly, mostly due to an overestimated stability of carbon in high oxidation states.

Stretching ofcis-formic acid: warm-up and cool-down as molecular work-out

“…For three atoms, HCN/HNC is the paradigmatic example 2. For four atoms, the simultaneous description of the nearly isoenergetic formaldehyde molecule and H 2 –CO complex is challenging 3,4. For five atoms, the cis – trans isomerism of formic acid is arguably one of the most interesting systems, calling for suitable experimental reference data for the higher-energy cis -form.…”

Setting up the HyDRA blind challenge for the microhydration of organic molecules

“…Constitutional relaxation is evidently not considered. Thus, the decomposition of formaldehyde into CO and H 2 is disregarded for the global minimum criterion, although it is exothermic by about 9 kJ mol −1 at low temperature 93 . The solutes always remain in the constitution given in Figure 2.…”

Benchmarking Quantum Chemical Methods: Are We Heading in the Right Direction?

“…Fori ntramolecular isomerism, the case of glucose may be mentioned, [54] although one should remember that the globalminimum structure for C 6 O 6 H 12 is ac ompletely different one. [63] Solvation preferences can be studied by intermolecular balance experiments as af unction of chemical substitution. [64] It turns out the balance between p-cloud and oxygen solvation of anisoles is not captured correctly by the M06-2X functional, whereas the B3LYP-D3 functional performs satisfactorily.Whether this is for agood reason can be found out by extending the data base.…”

“…Again, it is beneficial for the comparison to quantum chemistry to remove thermal excitation and the environment. For intramolecular isomerism, the case of glucose may be mentioned, although one should remember that the global‐minimum structure for C 6 O 6 H 12 is a completely different one . Solvation preferences can be studied by intermolecular balance experiments as a function of chemical substitution .…”