skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Classical tosylate/chloride leaving group approach supports a tetrahedral transition state for additions to trigonal carbon
Title: Classical tosylate/chloride leaving group approach supports a tetrahedral transition state for additions to trigonal carbon
The experimentally measured rates of solvolysis of 2-chloroethoxycarbonyl chloride (2-chloroethyl chloroformate, 3), 2-chloroethoxycarbonyl p-toluenesufonate (5), and phenoxycarbonyl p-toluenesulfonate (6) were followed at 25.0 °C in various pure and binary aqueous-organic solvents with varying degrees of polarity. An analysis of the rate constants for 3, 5, and 6, was carried out using the two-term extended Grunwald-Winstein equation and comparisons are made to the previously published results for ethyl and phenyl chloroformate esters. The kOTS/kCl rate ratios and the Grunwald-Winstein l/m ratios indicate the probability of a dominant bimolecular carbonyl-addition pathway in the more nucleophilic solvents. Nevertheless in 3 and 5, in the strongly hydrogen-bonding 70% and 50% HFIP mixtures, a side-by-side ionization mechanism is favored. Keywords: solvolysis, carbonyl-addition, phenyl chloroformate, ethyl chloroformate, 2-chloroethyl chloroformate, 2-chloroethoxycarbonyl p-toluenesulfonate, phenoxycarbonyl p-toluenesulfonate  more » « less
Award ID(s):
1757353
PAR ID:
10100601
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Trends in Organic Chemistry
Volume:
19
Issue:
1
ISSN:
0972-4362
Page Range / eLocation ID:
1-11
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Polyhedron)
    The synthesis of the bidentate Mo complex tetrachlorido[6-(3’-butylimidazolium-1’-yl)-2-(3’’-butylimidazol-1’’-yl-2’’-idene-κC2)phenyl-κC1]molybdenum(IV) 3 was carried out using the metalation followed by transmetalation methodology. The transmetallation process led to a bidentate complex after reaction of DCM with HNMe2 formed an acidic ammonium ion that protonated the bidentate complex. Optimization of the synthetic methodology provided the tetrachlorido[6-(3’-butylimidazolium-1’-yl)-2-(3’’-butylimidazol-1’’-yl-2’’-idene-κC2)phenyl-κC1]molybdenum(IV) complex in high yield. The crystal structure of the bidentate complex, 3, is reported herein. Attempts to avoid the acidic reaction conditions with different solvents or starting materials produced the bis-ligated Mo complex bis[2,6-bis(3’-butylimidazol-1’-yl-2’-idene-κC2)phenyl-κC1]molybdenum(IV) dichloride based on MS analysis. Electronic and coordinative unsaturation in the resulting bidentate complex, 3, open new possibilities for coordination of incoming substrates while also allowing access to the pincer-like motif via oxidative addition. Access to the interconversion of a NHC to/from imidazolium opens new avenues of non-innocent ligand pathways for proton shuttling in reactions such as nitrogen reduction to ammonia. 
    more » « less
  2. ; ; ; (, Acta Crystallographica Section E Crystallographic Communications)
    The title complex, (1,4,7,10,13,16-hexaoxacyclooctadecane-1κ6O)(μ-oxalato-1κ2O1,O2:2κ2O1′,O2′)triphenyl-2κ3C-potassium(I)tin(IV), [KSn(C6H5)3(C2O4)(C12H24O6)] or K[18-Crown-6][(C6H5)3SnO4C2], was synthesized. The complex consists of a potassium cation coordinated to the six oxygen atoms of a crown ether molecule and the two oxygen atoms of the oxalatotriphenylstannate anion. It crystallizes in the monoclinic crystal system within the space groupP21. The tin atom is coordinated by one chelating oxalate ligand and three phenyl groups, forming acis-trigonal–bipyramidal geometry around the tin atom. The cations and anions form ion pairs, linked through carbonyl coordination to the potassium atoms. The crystal structure features C—H...O hydrogen bonds between the oxygen atoms of the oxalate group and the hydrogen atoms of the phenyl groups, resulting in an infinite chain structure extending alonga-axis direction. The primary inter-chain interactions are van der Waals forces. 
    more » « less
  3. ; ; ; ; ; (, Acta Crystallographica Section E Crystallographic Communications)
    In the centrosymmetric title complexes, di-μ-acetato-bis({N,N-dimethyl-2-[phenyl(pyridin-2-yl)methylidene]hydrazine-1-carbothioamidato}zinc(II)), [Zn2(C15H15N4S)2(C2H3O2)2] (I), and di-μ-acetato-bis({N-ethyl-2-[phenyl(pyridin-2-yl)methylidene]hydrazine-1-carbothioamidato}zinc(II)), [Zn2(C16H17N4S)2(C2H3O2)2] (II), the zinc ions are chelated by theN,N,S-tridentate ligands and bridged by pairs of acetate ions. The acetate ion in (I) is disordered over two orientations in a 0.756 (6):0.244 (6) ratio, leading to different zinc coordination modes for the major (5-coordinate) and minor (6-coordinate) disorder components. Geometrical indices [τ5= 0.32 and 0.30 for (I) (major component) and (II), respectively] suggest the zinc coordination in these phases to be distorted square pyramidal. This study forms part of our aim to discern the mechanism of metal binding in these chelators, their specificity and selectivity, and to gain insight into the role of cellular zinc in physiological processes such as infection, immunity and cancer. 
    more » « less
  4. ; ; ; ; (, Acta Crystallographica Section C Structural Chemistry)
    The crystal structures of 2,3,4,6-tetra- O -benzoyl-β-D-galactopyranosyl-(1→4)-1,2,6-tri- O -benzoyl-β-D-glucopyranose ethyl acetate hemisolvate, C 61 H 50 O 18 ·0.5C 4 H 8 O 2 , and 1,2,4,6-tetra- O -benzoyl-β-D-glucopyranose acetone monosolvate, C 34 H 28 O 10 ·C 3 H 6 O, were determined and compared to those of methyl β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside (methyl β-lactoside) and methyl β-D-glucopyranoside hemihydrate, C 7 H 14 O 6 ·0.5H 2 O, to evaluate the effects of O -benzoylation on bond lengths, bond angles and torsion angles. In general, O -benzoylation exerts little effect on exo- and endocyclic C—C and endocyclic C—O bond lengths, but exocyclic C—O bonds involved in O -benzoylation are lengthened by 0.02–0.04 Å depending on the site of substitution. The conformation of the O -benzoyl side-chains is highly conserved, with the carbonyl O atom either eclipsing the H atom attached to a 2°-alcoholic C atom or bisecting the H—C—H bond angle of an 1°-alcoholic C atom. Of the three bonds that determine the side-chain geometry, the C—O bond involving the alcoholic C atom exhibits greater rotational variability than the remaining C—O and C—C bonds involving the carbonyl C atom. These findings are in good agreement with recent solution NMR studies of the O -acetyl side-chain conformation in saccharides. 
    more » « less
  5. ; (, IUCrData)
    In the title compound, C10H12N2O4, the four substituents lie out of the phenyl plane by varying degrees. The methyl C atom lies 0.019 (3) A ˚ out of plane, while the methoxy O and C atoms lie 0.067 (2) and 0.042 (3) A ˚ out of plane, respectively, with the C—C—O—C torsion angle being 3.3 (2). The plane of the nitro group is twisted out of the phenyl plane, forming a dihedral angle of 12.03 (9) with it. The acetamide substituent is twisted considerably more out of the phenyl plane, forming a dihedral angle of 47.24 (6) with it. In the extended structure, the acetamide NH group donates a hydrogen bond to an acetamide carbonyl O atom, thereby forming chains propagating in the [010] direction. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email