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According to the IUPAC definition of a hemiacetal, the R 1 and R 2 groups may or may not be hydrogen. In a hemiketal, both of these R-groups must not be hydrogen. Thus, hemiketals are regarded as a subclass of hemiacetals. [1] The prefix hemi, meaning half, refers to the one alcohol added to the carbonyl group.
The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1. This forms an intramolecular hemiacetal.If reaction is between the C-4 hydroxyl and the aldehyde, a furanose is formed instead. [1]
Generic structure of acetals. In organic chemistry, an acetal is a functional group with the connectivity R 2 C(OR') 2. Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each ...
C 8 H 7 ClO 2: benzyl chloroformate: 501-53-1 C 8 H 7 F 2 NO: difluoroacetanilide: 404-17-1 C 8 H 7 F 7 O 3: ethyl heptafluorobutanoylacetate: 336-62-9 C 8 H 7 I: iodocubane: 74725-77-2 C 8 H 7 IO 2: methyl 4-iodobenzoate: 619-44-3 C 8 H 7 N: benzeneacetonitrile: 140-29-4 C 8 H 7 N: indole: 120-72-9 C 8 H 7 N: indolizine: 274-40-8 C 8 H 7 NO ...
Hemithioacetal functional group. In organic chemistry, hemithioacetals (or thiohemiacetals) are organosulfur compounds with the general formula R−CH(−OH)−SR’.They are the sulfur analogues of the acetals, R−CH(−OH)−OR’, with an oxygen atom replaced by sulfur (as implied by the thio-prefix).
In organic chemistry, an acetyl group is a functional group denoted by the chemical formula −COCH 3 and the structure −C(=O)−CH 3.It is sometimes represented by the symbol Ac [5] [6] (not to be confused with the element actinium).
The mechanism is tentatively hypothesized to take place by the following steps: [7] The reduced di-iron coordinates oxygen, which oxidizes the iron and forms a peroxide species. The peroxide species attacks the aldehyde. An electron transfer coupled with cleavage of the peroxo species generates a hemi-acetal radical.
One method of pretreatment is to soak the wood with diluted acids (with concentrations around 4%). This converts the hemicellulose into monosaccharides. When pretreatment is done with bases (for instance sodium or potassium hydroxide) this destroys the structure of the lignin. [20] This changes the structure from crystalline to amorphous.