The effects of halogen substituents on structure, stability, and electronic properties of bicyclo[1.1.1]pentanylene at density functional theory

Abstract

In a quest to identify novel bicyclic carbenes, the effects of halogen substituents on the stability and reactivity of singlet (s) and triplet (t) forms of carbenes with one, two, and three carbenic centers (1-15) are compared and contrasted, at B3LYP/6-311++G** level of theory. All carbene scrutinized turn out as minima for showing no negative force constant on their energy surfaces. The highest stability (ΔE s-t ) and band gap (ΔE HOMO-LUMO ) belongs to carbene 11 (37.36 and 133.45 kcal/mol, respectively) with three carbenic centers. Such higher stabilization attributed to three coordinate covalent bonds with their carbenic centers. The nucleophilicity (N) for each series (1-5, 6-10, and 11-15) appears inverse correlation with our results of chemical potential (μ) values. Also, the N of the carbenic center is decreased due to the higher electronegativity of substituted halogens. In addition, the electrostatic potential (ESP) maps qualitatively confirm the relative N for our bicyclic carbenes.The aim of the present work was to assess the effects of halogen substituents on the stability (ΔE s-t ), ΔΕ HOMO-LUMO , N, electrophilicity (ω), and proton affinity (ΔE PA ). Finally, our investigation introduces carbene 1 s with high stability (ΔE s-t = 30.38 kcal/mol), N (3.438 eV), and negative ΔE PA (À244.94 kcal/mol) that can be applied as accumulated multidentate ligands. K E Y W O R D Sband gap, bicyclic carbene, coordinate covalent bond, stability | INTRODUCTIONCarbenes, in a Lewis sense, have two electrons not involved in bonding (singlet (s) or triplet state (t)) and two non-bonding orbitals into which to place those electrons. [1][2][3][4][5][6][7][8][9][10] The electronic structure and stability of a carbene are affected by the mesomeric or inductive effects of substituents attached to the carbenic center. [11][12][13][14][15] Goddard and coworkers have suggested certain simple, empirically corrected computational approaches to estimate s-t gaps, particularly for halo-substituted carbenes. [16][17][18][19] The substituents by changing the orbital hybridizations at the carbenic center affect the energetic separation between the formally non-bonding orbitals. The carbenic center might be expected to reduce its s character in a bonding orbital to electronegative atom (F) and provide a corresponding increase in s character to its other in-plane orbitals. The electronegative effect includes an increase in splitting between the carbon 2s and 2p orbitals as partial positive charge builds up on the

Completion of Crystallographic Data for the Series of 4-Halogenated-1H-pyrazoles: Crystal Structure Determination of 4-Iodo-1H-pyrazole and Spectroscopic Comparison

“…The series of 4-halogenated pyrazoles follow this trend with the most electronegative substituent, F, exhibiting the highest N-H stretching frequency in IR and the most upfield chemical shift in NMR; the least electronegative substituent, I, exhibited the opposite effect. While the substituent effect of aromatics have been studied (with benzene having been studied most extensively), the focus of papers has been on how halogens (usually represented by only Cl or Br) relate to other electron donating substituents, or how changing the position of a halide in relation to another substituent on the ring affects aromaticity [41][42][43][44][45][46]. To the best of our knowledge, the spectroscopy for a full series of halogenated pyrazoles has not been studied.…”