Methylene Groups, CH

Benzylidene derivatives. Compounds containing the. keto-methylene group (—CH CO) react with benzaldeliyde to yield benzylidene derivatives ... 

Composition and Analysis. Naturally occurring drying oils are triglycerides. The reactivity of the oils results fiotn the presence of esters of fatty acids with two or mure nonconjugated double bonds separated by single methylene groups. -CH=CHCHiCH=CH hose with two or more conjugated double bonds. Typical compositions of some of the more important oils are listed in Table I... 

A methyl group (CHj) is a primary carbon centre (attached to one carbon), a methylene group (CH ) is a secondary carbon centre (attached to the other carbons), a methine group (CH) is a tertiary carbon centre (attached to three other carbons) and a carbon centre with four alkyl substituents (C) is a quaternary carbon centre (attached to four other carbons) ... 

This oxidation proceeds readily if the methylene group is activated by linkage to (a) a carbonyl group, (b) an aromatic ring (c) an olefine link also activates adjacent CH2 and CH groups. 

These and other studies of the relative substituent effects of X and CH X in nitration were considered in terms of the transmission factor a of the methylene group. To avoid complications from conjugative interactions, attention was focussed mainly on substitution at the meta-position, and ct was defined in terms of partial rate factors by the equation ... 

As just noted (Section 2 7) CH3 is called a methyl group In addition to having methyl groups at both ends n butane contains two CH2 or methylene groups Isobutane con tains three methyl groups bonded to a CH unit The CH unit is called a methme group... 

Methine group (Section 2 8) The group CH Methylene group (Section 2 8) The group —CH2—... 

The difference between 2-CH2 and 6-CH2 is shown by the nuclear Overhauser enhancement (NOE) on the proton at Su = 6.67, if the methylene protons at 5 = 2.87 are irradiated. The assignment of the methylene C atoms can be read from the CH COSY segment. The C atoms which are in close proximity to one another at 5c = 113.3 and 113.8 belong to C-5 and C-7. Carbon atom C-5 is distinguished from C-7 by the pseudo-quartet splitting CJqh = 3.4 Hz to 1-H and A-H2) that involves the methylene group in the ortho position. 

Rather large HH coupling constants in the aliphatics range (72.5 and 15.0 Hz) indicate geminal methyl protons in rings. In order to establish clearly the relevant AB systems, it makes sense first to interpret the CH COSY diagram (Table 52.1). From this, the compound contains two methylene groups, A and B. 

The latter, which contains the group CO.CH, .C,H, behaves like malonic ester, the hj drogen of the methylene group being replaceable by sodium, and hence by alkyl groups. 

Compounds of the type HC=C—CH=CHXR are not involved in a primary reaction with weak nucleophiles such as CH acids meanwhile, a final (secondary) cyclization with participation of active methylene groups happens to be feasible. Evidently, in most cases the energy gain in the heteroaromatic system realization is the decisive factor (81UK1252). 

Draw resonance structures for the trimethylenemethane anion C(CH,) 2 in which a central carbon atom is attached to thi ee CH, groups (CH, groups are referred to as methylene). 

Formulas for the analysis of surface sum-frequency generation spectrum by CH stretching modes of methyl and methylene groups. J. Chem. Phys., 96, 997-1004. 

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