Muon‐Substituted Malonaldehyde: Transforming a Transition State into a Stable Structure by Isotope Substitution

Abstract

Isotopes ubstitutionsa re usually conceived to play am arginal role on the structure and bondingp attern of molecules. However,arecent study [Angew.C hem. Int. Ed. 2014, 53,1 3706-13709; Angew.C hem. 2014, 126,1 3925-13929]f urther demonstrates that upon replacing ap roton with ap ositively charged muon, as the lightest radioisotope of hydrogen, radical changes in the nature of the structure and bonding of certains peciesm ay take place. The present report is ap rimary attemptt oi ntroduce another example of structural transformation on the basis of the malonaldehyde system.A ccordingly,u pon replacing the protonb etween the two oxygen atoms of malonaldehydew ith the positively charged muon as erious structuralt ransformationi so bserved. By using the ab initio nuclear-electronic orbitaln onBorn-Oppenheimer procedure, the nuclear configuration of the muon-substituted speciesi sd erived. The resulting nuclear configuration is much more similart ot he transition state of the proton transferi nm alonaldehyde rather than to the stable configuration of malonaldehyde. The comparison of the "atoms in molecules" (AIM) structureoft he muon-substituted malonaldehyde and the AIM structureo ft he stable and the transition-state configurations of malonaldehyde also unequivocally demonstrates substantial similarities of the muon-substituted malonaldehydet ot he transition state.

Some implications of the Hartree product treatment of the quantum nuclei in the ab initio nuclear–electronic orbital methodology

“…, which has also been used in some previous ab initio NEO-HF calculations [23][24][25][26]36], is employed herein. In this function the two parameters, to be determined for each quantum nucleus, are the exponent, n  , and the center of the location of the function in space, , n c R  .…”

“…The Nuclear-electronic orbital (NEO) is particularly a promising non-BO ab initio methodology since various types of the NEO wavefunctions have been proposed with varying degree of complexity [1,[10][11][12][13][14][15][16][17][18][19][20][21][22]. Very recently, the NEO has also been successfully utilized for molecules containing exotic light quantum particles like the positively charged muons [23][24][25][26]. In this methodology certain types of nuclei or exotic light quantum particles are treated as quantum waves while adequate numbers of clamped nuclei are retained to avoid the complications emerging from treating total translational and rotational dynamics [27,28].…”

Revisiting the foundations of the quantum theory of atoms in molecules: Some open problems

“…Starting from a decade ago, inspired by these exchanges, the present author and his coworkers reconsidered the mathematical foundations of the QTAIM in detail trying to resolve some issues put forward by critics of the QTAIM formalism . Interestingly, as a byproduct, this reconsideration eventually gave rise to an extended version of the QTAIM, finally termed the multi‐component QTAIM, which widens the applications of the AIM analysis beyond the Born‐Oppenheimer paradigm as well as exotic molecular species …”

Uncontracted basis sets for ab initio calculations of muonic atoms and molecules

“…For example, the positive muon can replace the proton in a hydrogen atom to yield a light isotope of hydrogen called muonium. The muonium atom can then become a part of molecules and give rise to structural changes . In addition, positive muons can localize in condensed matter at negatively charged sites .…”