Intramolecular hydrogen bonding protects the hydroxyl group from attack by fluctuating solvent forces

2020 ◽  
Vol 152 (7) ◽  
pp. 074502
Author(s):  
Amit Akiva ◽  
Lev Chuntonov
Keyword(s):  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Intramolecular Hydrogen

Molecular and crystal structure of azadirachtin-H

1996 ◽  
Vol 52 (1) ◽  
pp. 145-150 ◽  
Author(s):  
T. R. Govindachari ◽  
Geetha Gopalakrishnan ◽  
S. S. Rajan ◽  
V. Kabaleeswaran ◽  
L. Lessinger
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Inhibiting Activity ◽  
Nmr Studies ◽  
Rotation Axes ◽  
Intramolecular Hydrogen ◽  
Azadirachtin A

Azadirachtin-H, isolated from the seed kernels of Azadirachta indica (neem), crystallizes in space group I4, Z = 8, with disordered ethyl acetate solvent filling channels along the fourfold rotation axes. The crystal structure determination showed that the previously reported molecular structure deduced from NMR studies was correct except for the stereochemistry at C(11). Azadirachtin-H, which belongs to a group of C-seco-tetranortriterpenoids (C-seco-limonoids) of great interest for their insect antifeedant and ecdysis-inhibiting activity, has some unusual features: the absence of a carbomethoxy group at C(11); the presence of a cyclic hemiacetal function at C(11); the α-orientation of the hydroxyl group on C(11), opposite to that in all other known azadirachtins with a hydroxyl group on C(11), except azadirachtin-I. There is no intramolecular hydrogen bonding. In this crystal the rotation of the two major moieties of the azadirachtin-H molecule about the single connecting C(8)—C(14) bond is quite different from that in azadirachtin-A, whose crystal structure has recently been determined.

2-Substituted and 2,6-disubstituted 1,4-benzoquinone 4-oximes ('p-nitrosophenols')

1969 ◽  
Vol 22 (5) ◽  
pp. 935 ◽  
Author(s):  
RK Norris ◽  
S Sternhell
Keyword(s):  
Hydrogen Bonding ◽  
Physical Properties ◽  
Intramolecular Hydrogen Bonding ◽  
Tautomeric Equilibrium ◽  
Phenolic Hydroxyl ◽  
Hydroxyl Group ◽  
Electronic Effects ◽  
Intramolecular Hydrogen

The preparation and physical properties of 27 compounds in the title series are described. Tautomerism, syn-anti isomerism, N.M.R. parameters, and the mechanism of isomerization are discussed. In this series of derivatives, the tautomeric equilibrium in dioxan solutions lies heavily towards the oxime form unless intramolecular hydrogen bonding between the substituent at C2 (or C6) and the phenolic hydroxyl group of the nitroso form is possible. The substituents at C2 (and C6) influence the position of the syn-anti equilibrium in the quinone monoxime forms through electronic effects.

The proton affinities and deprotonation enthalpies of β-D-fructopyranose and α-L-sorbopyranose

1991 ◽  
Vol 69 (12) ◽  
pp. 1917-1928 ◽  
Author(s):  
Robert J. Woods ◽  
Walter A. Szarek ◽  
Vedene H. Smith Jr.
Keyword(s):  
Hydrogen Bonding ◽  
Oxygen Atom ◽  
Intramolecular Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Proton Affinities ◽  
Naturally Occurring ◽  
Acid Catalyzed ◽  
Acids And Bases ◽  
Intramolecular Hydrogen ◽  
Hydrolysis Of

The proton affinities (PAs) and deprotonation enthalpies (DPEs) were calculated for the pyranoid forms of two naturally occurring sugars, D-fructose and L-sorbose. In both molecules the PAs of the primary hydroxyl group (HO-1), the anomeric hydroxyl group (HO-2), and the ring-oxygen atom (O-6) were calculated, as were the DPEs of HO-1 and HO-2. The stabilities of the conjugate acids and bases of these sugars are enhanced by the presence of intramolecular hydrogen bonding, a feature that is significant in explaining the differences in sweetness and the rates of mutarotation of the title compounds, as well as the differences in the rates of acid-catalyzed hydrolysis of ketopyranosides. Key words: proton affinity, deprotonation enthalpy, ab initio calculations, AM1, hexuloses.

scholarly journals Regioselective Reduction of 1H-1,2,3-Triazole Diesters

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5589
Author(s):  
Christopher R. Butler ◽  
Justin Bendesky ◽  
Allen Milton Schoffstall
Keyword(s):  
Organic Chemistry ◽  
Hydrogen Bonding ◽  
Sodium Borohydride ◽  
Intramolecular Hydrogen Bonding ◽  
Ester Group ◽  
Hydroxyl Group ◽  
Carbonyl Carbon ◽  
Enhancing Effect ◽  
Time Required ◽  
Intramolecular Hydrogen

Regioselective reactions can play pivotal roles in synthetic organic chemistry. The reduction of several 1-substituted 1,2,3-triazole 4,5-diesters by sodium borohydride has been found to be regioselective, with the C(5) ester groups being more reactive towards reduction than the C(4) ester groups. The amount of sodium borohydride and reaction time required for reduction varied greatly depending on the N(1)-substituent. The presence of a β-hydroxyl group on the N(1)-substituent was seen to have a rate enhancing effect on the reduction of the C(5) ester group. The regioselective reduction was attributed to the lower electron densities of the C(5) and the C(5) ester carbonyl carbon of the 1,2,3-triazole, which were further lowered in cases involving intramolecular hydrogen bonding.

Intramolecular hydrogen bonding in cycloalkane-1,2-diol monoacetates

1968 ◽  
Vol 46 (15) ◽  
pp. 2567-2575 ◽  
Author(s):  
Robert W. Wright ◽  
R. H. Marchessault
Keyword(s):  
Hydrogen Bonding ◽  
Frequency Band ◽  
High Frequency ◽  
Intramolecular Hydrogen Bonding ◽  
Carbonyl Oxygen ◽  
Hydroxyl Group ◽  
High Frequency Band ◽  
Absorption Bands ◽  
Hydroxyl Absorption ◽  
Intramolecular Hydrogen

Intramolecular hydrogen bonding in cyclopentane- and cyclohexane-1,2-diol monoacetates was studied by high resolution infrared spectroscopy in the 3μ region. Intramolecular hydrogen bonding was exhibited by all compounds and the data are interpreted in terms of preferred conformations, assuming the acetate group to be exclusively in the "planar trans" form.trans-Cyclopentane-1,2-diol monoacetate exhibited two hydroxyl absorption bands. One band was assigned to free hydroxyl stretching and the other to hydrogen bonding with the carbonyl oxygen so that an equilibrium between two ring conformations must be assumed to exist in solution. With cis-cyclopentane-1,2-diol monoacetate only a strong high frequency band was observed, and this was attributed to hydrogen bonding to the alkoxyl oxygen.trans- and cis-cyclohexane-1,2-diol monoacetate both exhibited two hydroxyl absorption bands. With the former, the hydroxyl group was assumed to be exclusively in an equatorial position to permit hydrogen bonding to both the alkoxyl and carbonyl oxygens. Similarly, in the latter, the high frequency band was attributed to hydrogen bonding to the alkoxyl oxygen atom while the low frequency band was assigned to hydrogen bonding to the carbonyl oxygen.

Differential reactivity of carbohydrate hydroxyls in glycosylations. I. Intramolecular interaction of the 5′-hydroxyl group with the heteroaromatic base in a model compound of 2′-deoxycytidine

1992 ◽  
Vol 70 (9) ◽  
pp. 2434-2448 ◽  
Author(s):  
Ting-Hua Tang ◽  
Dennis M. Whitfield ◽  
Stephen P. Douglas ◽  
Jiri J. Krepinsky ◽  
Imre G. Csizmadia
Keyword(s):  
Hydrogen Bonding ◽  
Lewis Acids ◽  
Potential Energy Surfaces ◽  
Model Compound ◽  
Intramolecular Interaction ◽  
Topological Analysis ◽  
Intramolecular Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bonded

It is a well-recognized conjecture that the unusual reactivity of certain carbohydrate hydroxyls in glycosylation reactions is due to non-covalent intramolecular bonding interactions involving that hydroxyl. A model compound 1-[β-D-2′,3′-dideoxyribofuranosyl]-2-(1H)-pyrimidinone, which is related to the poor glycosyl acceptor 2′-deoxy-3′-O,4-N-diacetylcytidine (1), has been studied in order to assess the effects of hydrogen bonding involving 05′—H and the heteroaromatic system present in the molecule. The conformational potential energy surfaces of the model compound (lacking only the acetoxy at C3′ and the acetamido at C4) were calculated, using semiempirical (PM3) and abinitio (STO-3G) methods. The [Formula: see text] intramolecular hydrogen-bonded syn conformation of the model compound is the global minimum at the abinitio level of theory. The existence of this intramolecular hydrogen bonding was confirmed, theoretically, by Bader-type topological analysis of charge distribution at the 3-21G**//STO-3G level of theory. Such a conformation of the model compound strongly resembles that found for 1 by NMR in CD2Cl2 solution. The complex formation between this model compound and BF3 was also studied at the STO-3G, 3-21G**//STO-3G, and 6-31G**//STO-3G levels of theory. The results explain why glycosylation of hydrogen-bonded substrates succeeds when promoted by Lewis acids.

Theoretical study of intramolecular hydrogen bonding and molecular geometry of 2-trifluoromethylphenol

10.1002/jcc.2 ◽  
1996 ◽  
Vol 17 (16) ◽  
pp. 1804-1819 ◽  
Author(s):  
Attila Kov�cs ◽  
Istv�n Kolossv�ry ◽  
G�bor I. Csonka ◽  
Istv�n Hargittai
Keyword(s):  
Hydrogen Bonding ◽  
Theoretical Study ◽  
Molecular Geometry ◽  
Intramolecular Hydrogen Bonding ◽  
Intramolecular Hydrogen
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