N -protonated and O -protonated tautomers of 1-azabicyclo[3.3.1]nonan-2-one: observation of individual 13 C-NMR carbonyl peaks and comparisons with protonated tautomers of planar and other distorted lactams

Amide nitrogen pyramidalization changes lactam amide spinning

Although cis-trans lactam amide rotation is fundamentally important, it has been little studied, except for a report on peptide-based lactams. Here, we find a consistent relationship between the lactam amide cis/trans ratios and the rotation rates between the trans and cis lactam amides upon the lactam chain length of the stapling side-chain of two 7-azabicyclo[2.2.1]heptane bicyclic units, linked through a non-planar amide bond. That is, as the chain length increased, the rotational rate of trans to cis lactam amide was decreased, and consequently the trans ratio was increased. This chain length-dependency of the lactam amide isomerization and our simulation studies support the idea that the present lactam amides can spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization. The tilting direction of the pyramidal amide nitrogen atom of the bicyclic systems is synchronized with the direction of the semicircle-rotation of the amide.

Cis-trans lactam amide rotation is a fundamental process and its understanding might aid molecular design. Here, the authors report the synthesis and study of bicyclic lactams which undergo spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization.

Does hydrohalic acid HX (X = F, Cl) form true N-protonated twisted amide salts? Effects of anions on the ion-pair interactions and on the amide moiety in N-protonated tricyclic twisted amide salts

The [BF₄]⁻ and [RSO₃]⁻ anions interact with N-protonated amide cations through N–H⋯F and N–H⋯O strong hydrogen bonds and hydrohalic acids form very weak N⋯H–X hydrogen bonds.

Protonated heterocyclic derivatives of cyclopropane and cyclopropanone: classical species, alternate sites, and ring fragmentation

A computational study has been performed for protonated oxygen- or nitrogen-containing heterocyclic derivatives of cyclopropane and cyclopropanone. We have searched for the most stable conformations of the protonated species using density functional theory with the B3LYP functional and the 6-31G(2df,p) basis set. More accurate enthalpy values were obtained from G4 calculations. Proton affinities and gas-phase basicities were accordingly derived.

Theoretical insights into structure, bonding, reactivity and importance of ion-pair interactions in Kirby's tetrafluoroboric acid salts of twisted amides

The hydrolysis of amide 1 is more exothermic and is more favorable than amides 2 and 3 with bridgehead methyl.

Electrospray ionization (ESI) fragmentations and dimethyldioxirane reactivities of three diverse lactams having full, half, and zero resonance energies

Three lactams having, respectively, ~20, ~10, and 0 kcal/mol of resonance energy have been subjected to electrospray ionization mass spectrometry (ESI/MS) as well as to attempted reaction with dimethyldioxirane (DMDO). The ESI/MS for all three lactams are consistent with fragmentation from the N-protonated, rather than the O-protonated tautomer. Each exhibits a unique fragmentation pathway. DFT calculations are employed to provide insights concerning these pathways. N-Ethyl-2-pyrrolidinone and 1-azabicyclo[3.3.1]nonan-2-one, the full- and half-resonance lactams, are unreactive with DMDO. The "Kirby lactam" (3,5,7-trimethyl-1-azaadamantan-2-one) has zero resonance energy and reacts rapidly with DMDO to generate a mixture of reaction products. The structure assigned to one of these is the 2,2-dihydroxy-N-oxide, thought to be stabilized by intramolecular hydrogen bonding and buttressing by the methyl substituents. A reasonable pathway to this derivative might involve formation of an extremely labile N-oxide, in a purely formal sense, an example of the hitherto-unknown amide N-oxides, followed by hydration with traces of moisture.