The six-membered ring subunit was transformed from an acetal, which was obtained by an intramolecular 1, 4-addition of a presumed hemiacetal intermediate.
22.
Lactaldehyde exists in several forms : in open-chain form and as cyclic hemiacetal; in solution and in crystal forms; as monomer and as dimer.
23.
Generally, Benedict's test detects the presence of aldehydes, alpha-hydroxy-ketones, also by hemiacetal, including those that occur in certain ketoses.
24.
Cellobiose has eight free alcohol ( OH ) groups, one acetal linkage and one hemiacetal linkage, which give rise to strong inter-and intramolecular hydrogen bonds.
25.
In some cases however, stable cyclic hemiacetals and hemiketals, called lactols, can be readily formed, especially when 5-and 6-membered rings are possible.
26.
When the hemiacetal group is reformed, the OH group on C-5 may attack either of the two stereochemically distinct sides of the aldehyde group on C-1.
27.
(Disaccharides may also react, but the reaction is much slower . ) The aldehyde group of the monosaccharide which normally forms a cyclic hemiacetal is oxidized to the carboxylate.
28.
A convenient form of the reagent for use in the laboratory is its bis ( hemiacetal ) with ethylene glycol, 1, 4-dioxane-2, 3-diol.
29.
In organic synthesis the use of cyclopropanone itself is substituted by that of synthons like acetals " cyclopropanone ethyl hemiacetal " or " cyclopropanone ethyl trimethylsilyl acetal ".
30.
In this case, the use of trifluoroperacetic acid derived from hydrogen peroxide, which therefore presumably contained traces of water, gave mostly a hemiacetal rather than the closed-ring dioxolane.
