Abstract:The microwave spectrum of the cyclopropane-ammonia (CsHs* 14NHs) complex has been observed using a pulsed nozzle, Fourier-transform microwave spectrometer. The spectrum is characteristic of a symmetric top, IS,,= 2668.7 16 l(4), with free internal rotation of the NHs subunit. The spectra of the CsHs*r5NHs, CsDs*r5NHs, and CSHe*'4NDs isotopomers were also measured. This gives a structure in which the nitrogen of the ammonia interacts with the top of the cyclopropane ring, resulting in a stacked structure with R… Show more
“… a Values obtained from ref . b PA is the proton affinity of the free amine monomer in units of kcal/mol obtained from ref .…”
Section: Discussionmentioning
confidence: 99%
“…Little work has been done on complexes of cyclopropane with non-hydrogen donor moieties. Recently, however, we found a new structure for cyclopropane complexes with the study of the cyclopropane−ammonia complex . The structure of CYC·NH 3 is stacked with the lone pair of the nitrogen atom pointing toward the center of the cyclopropane ring.…”
The rotational spectra of the cyclopropane-trimethylamine (CYC‚TMA) and cyclopropane-dimethylamine (CYC‚DMA) complexes have been observed using a pulsed nozzle, Fourier transform microwave spectrometer. The spectrum of CYC‚TMA is characteristic of a symmetric top, B o ) 1172.2800(1) MHz. Unlike the symmetric top complex of cyclopropane-ammonia (Chem. Phys. Lett. 1994, 218, 349-352), the CYC‚TMA complex did not exhibit effects from internal rotation about the C 3 axis. The CYC‚DMA complex has an asymmetric top spectrum with A ) 5095.137(9) MHz, B ) 1456.477(2) MHz, and C ) 1301.365(1) MHz. Both structures have the amine sitting above the ring, with the lone pair pointing toward the cyclopropane. A comprehensive discussion of the three cyclopropane-amine complexes in terms of spectral characteristics and constants, structure, strength, and dynamics is included, as well as an effort to understand the origin of these interactions from an examination of the electrostatic potential of cyclopropane. We also contrast the cyclopropane-base complexes with the cyclopropaneacid complexes found in the literature.
“… a Values obtained from ref . b PA is the proton affinity of the free amine monomer in units of kcal/mol obtained from ref .…”
Section: Discussionmentioning
confidence: 99%
“…Little work has been done on complexes of cyclopropane with non-hydrogen donor moieties. Recently, however, we found a new structure for cyclopropane complexes with the study of the cyclopropane−ammonia complex . The structure of CYC·NH 3 is stacked with the lone pair of the nitrogen atom pointing toward the center of the cyclopropane ring.…”
The rotational spectra of the cyclopropane-trimethylamine (CYC‚TMA) and cyclopropane-dimethylamine (CYC‚DMA) complexes have been observed using a pulsed nozzle, Fourier transform microwave spectrometer. The spectrum of CYC‚TMA is characteristic of a symmetric top, B o ) 1172.2800(1) MHz. Unlike the symmetric top complex of cyclopropane-ammonia (Chem. Phys. Lett. 1994, 218, 349-352), the CYC‚TMA complex did not exhibit effects from internal rotation about the C 3 axis. The CYC‚DMA complex has an asymmetric top spectrum with A ) 5095.137(9) MHz, B ) 1456.477(2) MHz, and C ) 1301.365(1) MHz. Both structures have the amine sitting above the ring, with the lone pair pointing toward the cyclopropane. A comprehensive discussion of the three cyclopropane-amine complexes in terms of spectral characteristics and constants, structure, strength, and dynamics is included, as well as an effort to understand the origin of these interactions from an examination of the electrostatic potential of cyclopropane. We also contrast the cyclopropane-base complexes with the cyclopropaneacid complexes found in the literature.
“…Complexes of cyclopropane ( 1 ) with various electrophiles and nucleophiles exhibit unusual molecular structures ( 2 − 4 ). − Computations on corner- ( 2a-asym C s , 2a-sym C s ) and edge-protonated cyclopropane ( 3a , C 2 v ) reveal an extremely flat potential energy surface . The ability of cyclopropanes to participate as hydrogen-bonding proton acceptors, first demonstrated inter- and intramolecularly by Schleyer et al using IR spectroscopy, has been confirmed recently by MW spectroscopy. − Like the π-systems in unsaturated hydrocarbons, the cyclopropane “bent bonds” 7 act (edge coordination mode 3 ) as proton acceptors for HOR, H 2 O, HF, HCl, and HCN .…”
Section: Introductionmentioning
confidence: 98%
“…The breaking of hydrogen bonds between water molecules by cyclopropane ( 1 ) is said to be responsible for the anaesthetic activity of 1 . However, in weaker van der Waals complexes, NH 3 , HNMe 2 , and NMe 3 10 are located above the cyclopropane ring plane (face coordination mode 4 ). …”
The short Li-C distances (Li 1 -C 2 ) 2.615(3) Å, Li 1 -C 3 ) 2.644(3) Å) in the X-ray crystal structure of [Li-O-C(Me)-(c-CHCH 2 CH 2 ) 2 ] 6 (7) 6 characterize Li-cyclopropane edge coordinations. The Li-cyclopropane interactions increase the C 2 -C 3 distances (1.519(3) Å) relative to those of the free cyclopropyl edges (C 2 -C 4 ) C 6 -C 7 ) 1.499(2) Å) by 0.02 Å. The bent bonds of cyclopropane give rise to an electrostatic potential pattern, which strongly favors edge coordination as is observed experimentally in (7) 6 , but also permits a metastable Li + face complex. The cyclopropane edge also is the favored site for hydrogen bonding, but not for protonation. The C-C bond length elongations, the coordination energies E coord , and the charge redistributions upon metal cation edge interactions all are related to the distances between the cyclopropane C-C bond centers and the cations. This is evaluated for the alkali metal cation-cyclopropane complexes (cation ) Li + to Cs + ). More generally, the cyclopropane C-C bond length variations can be employed as a structural measure for the magnitudes of electrostatic interactions.
“…The forces of the intermolecular and intramolecular hydrogen bonds may ensure that there is no free rotation around the N–C(α) bond. The gas phase rotation barrier (≈10–15 kJ/mol) of amine group is much lower than the rotation barrier in solids (≈20–60 kJ/mol) . In solids, the rotation energy barrier is the energy to break the hydrogen bonds with very little rearrangements .…”
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