equatorial substituent
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2003 ◽  
Vol 59 (11) ◽  
pp. o638-o640
Author(s):  
Roger A. Lalancette ◽  
Hugh W. Thompson

The asymmetric unit of the title compound, C9H14O3, consists of two molecules having conformations that differ by 121.7 (4)° in their rotation about the equatorial substituent bond, so that the side chain extends away from the ring in different directions in the two species. The hydrogen-bonding mode is acid-to-acid dimerization. However, despite the centrosymmetric space group (P\overline 1), the dimers are asymmetric, formed by pairing molecules of identical chirality but differing conformational type [O...O = 2.681 (2) and 2.654 (2) Å, and O—H...O = 175 (3) and 176 (3)°]. Two intermolecular C—H...O=C close contacts exist, involving the ketone group of one of the molecules. A two-phase technique is described for slow reforming of crystals of a water-insoluble acid by contact with an aqueous solution of its water-soluble salt.



2002 ◽  
Vol 67 (5) ◽  
pp. 622-644 ◽  
Author(s):  
Michaela Hamerníková ◽  
Jaroslav Havlíček ◽  
Hana Votavová ◽  
Karel Kefurt

Three isomeric 6-amino-3,6-dideoxyhexono-1,6-lactams of D-ribo (1a), L-lyxo (2a) and L-arabino (3a) configuration were synthesized via the corresponding 6-azido-3,6-dideoxyhexoses starting from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose. Conformation of lactams 1a, 2a and 3a and their tri-O-acetyl derivatives 1b, 2b and 3b was studied using NMR spectroscopy. CD spectra of the lactams 1a-3a, together with the D-xylo diastereoisomer 4a, were measured and interpreted according to semiempirical rules. NMR and CD measurements confirmed the chair conformation with an equatorial substituent on C-2 as prevailing for the all measured lactams.



1995 ◽  
Vol 34 (16) ◽  
pp. 4268-4270 ◽  
Author(s):  
Jiong Huang ◽  
Lily Lee ◽  
Brian S. Haggerty ◽  
Arnold L. Rheingold ◽  
Marc A. Walters




1990 ◽  
Vol 112 (11) ◽  
pp. 4601-4602 ◽  
Author(s):  
Jan Woning ◽  
Lee M. Daniels ◽  
John G. Verkade


1987 ◽  
Vol 40 (1) ◽  
pp. 79 ◽  
Author(s):  
SR Johns ◽  
JA Lamberton ◽  
TC Morton ◽  
H Suares ◽  
RI Willing

Re-examination of the optically active long-chain 5-hydroxycyclohex-2-enones of Campnosperma species has confirmed the former structural assignments, except that in Tigaso oil both the 5- hydroxycyclohex-2-enones and the phenolic components contain a significant (35-40%) proportion of compounds with di-unsaturation in the C19-chain. Further study has been made of the conversion of (-)-endo-4-hexadecyl-l-hydroxybicyclo[3.3.l]nonane-3,7-dione (10) into a mixture of an optically inactive and optically active β- diketones. The major product from this reaction is (�)-5-(1-acetylheptadecy1)cyclohexane-1,3-dione (1l), which on methylation with diazomethane gives a mixture of two diastereoisomeric Omethyl ethers. These undergo cyclization to give a mixture of two epimeric 4-hexadecyl-l-methoxybicyclo[3.3.l]nonane-3,7-diones, (16) and (17), but reduction of the enol ethers followed by cyclization leads to an epimeric mixture of 4 hexadecylbicyclo [3.3.l]nonane-3,7-dion, (21) and (22). A detailed n.m.r. study of the bicyclo[3.3.l]nonane-3,7-diones, (10), (16), (17), (21), (22), (27) and (28), indicates that all have a chair-chair conformation, and also shows which of these compounds have an equatorial substituent, (10), (16), (21) and (27), and which an axial, (17), (22) and (28), at C4. Reduction of the bicyclo[3.3.1]nonane-3,7-diones with sodium borohydride gives oxaadamantane derivatives, and reduction of one diastereoisomeric β- diketone Omethyl ether gives a high yield of (�)-endo-4-hexadecyl-exo-3-methyl-2-oxabicyclo[3.3.l]nonane-7-one (25), the structure of which has been fully derived from n.m.r. study.



1974 ◽  
Vol 52 (24) ◽  
pp. 4095-4100 ◽  
Author(s):  
T. P. Forrest

Proton coupling constants have been used in calculating dihedral angles of vicinal gauche protons in variety of pyranose derivatives of glucose, mannose, arabinose, xylose, altrose, and galactose. The calculations involve the use of a formula which was derived from a correlation of the coupling constants of ethane derivatives with the electronegativities of substituents and their orientation relative to the coupled protons.The results indicate that the formula has general applicability and gives more reasonable values than a Karplus equation in which the constants have been adjusted to fit some compounds of the series. The calculated dihedral angles indicate that an equatorial substituent generally causes little distortion of dihedral angles, whereas an axial substituent generally causes the equatorial proton on the same carbon to have a smaller than normal dihedral angle with the adjacent axial proton and a larger than normal dihedral angle with the adjacent equatorial proton.



1971 ◽  
Vol 49 (4) ◽  
pp. 588-593 ◽  
Author(s):  
R. Burton ◽  
L. D. Hall ◽  
P. R. Steiner

The 13C chemical shifts of acetate- and methoxyl-methyl substituents of several pyranose carbohydrate derivatives have been measured by the 1H–{13C} INDOR technique. The chemical shifts (δ13C) of anomeric methoxyl-methyl resonances fall into two groups: for α-anomers (axial substituent), δ13C = 55.12–56.63 p.p.m.; for β-anomers (equatorial substituent), δ13C = 56.63–8.69 p.p.m. O-Acetyl-methyl shifts fall between 20.54–20.72 p.p.m. and N-acetyl-methyl shifts were detected between 22.98–23.08 p.p.m.



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