With Loss of a Methyl Group

Dimethoxy tellurium tetrafluoride methylates pyridine , imidazole, potassium phthal-imide, and dimethylformamide. When alkoxy methoxy tellurium tetrafluorides were reacted with pyridine, only the methyl group was transferred to the base.  

---

Penton and Zollinger (1979, 1981 b) reported that this could indeed be the case. The coupling reactions of 3-methylaniline and A,7V-dimethylaniline with 4-methoxy-benzenediazonium tetrafluoroborate in dry acetonitrile showed a number of unusual characteristics, in particular an increase in the kinetic deuterium isotope effect with temperature. C-coupling occurs predominantly (>86% for 3-methylaniline), but on addition of tert-butylammonium chloride the rate became much faster, and triazenes were predominantly formed (with loss of a methyl group in the case of A V-di-methylaniline). Therefore, the initial attack of the diazonium ion is probably at the amine N-atom, and aminoazo formation occurs via rearrangement. 

The lactam-lactim tautomerism of hydroxyquinazolines is reflected in their chemical reactivity. Thus they are chlorinated to 4-chloro-quinazolines (see Section VI,A), and both 0- and A-methylation have been observed. When a substituent is already present on a nitrogen atom, as in 3-methyl-4(3i7)quinazolinone, chlorination gives 4-chloroquinazoline with loss of the methyl group (see la). 2-... 

In the mass spectrum (Figure 6) of 3-deoxy-l,2 5,6-di-0-isopropyli-dene-D-xt/Zo-hexofuranose (9) the fragmentations described above are found at m/e 229, 171, 143, 111, and 101. The fragments at m/e 143 and 101 arise by cleavage of C-4-C-5 with charge retention on C-4 and C-5, respectively (see Equations 17 and 18). Scheme 2 summarizes the losses of a methyl group, acetone from the second cyclic ketal function, and... 

The molecular ions decrease in intensity with increasing chain length but are still detectable at C40. In contrast to branched alkanes, the loss of a methyl group is not favored for n-alkanes. Usually the... 

The lanthanide ions have been reacted with trimethoxymethane, HC(OM3)3, with some interesting results (105). Most of the major product ions are the monomethoxide or dimethoxide ions, [MOMe]+ or [M(OMe)2]+. There are no ions that abstract hydrogen to form hydride ions, [MH]+, or ions that abstract CO to form [MCO]+ ions. The ions [M(CO)H(OMe)2]+ are observed for Eu+, Gd+, and Tb+, suggesting the unusual loss of a methyl group. 

All six spectra showed strong fragment ions at m/e 205 corresponding to loss of a methyl group. The spectral features are in general agreement with those of trimethyl or methylethylphen-anthrene anthracene. Exact isomeric structures could not be determined because many isomers of the methyl-, C2-alkyl-, and Cg-alkylphenanthrene/anthracene are possible but only a few methylphenanthrene/anthracene standards were available to us. 

The mesoionic pyrazoles 116 and 117123 on heating with DMAD yield the pyrazolium fumaric esters 118 and 119 with concomitant loss of a methyl group.124... 

An analogous ring contraction-carbon elimination reaction with Ni-etioporphyrin would require loss of a methyl group which is energetically prohibitive. Formation of a methyl carbonium ion, for example, is energetically 50 kcal/mole higher than the corresponding xylyl carbonium ion. 

The other five molecules which were identified using continuous-flow HPLC-1 H NMR spectroscopy at an observation frequency of 400 MHz were a-tocoenol with a mass of 428 (a double bond at Cl 1 ), a-tocotrienol with a mass of 424 (double bonds at C3, Cl and Cll ), (3-tocotrienol with a mass of 410 (double bonds at C3, Cl and Cl V, but with loss of a methyl on the phenyl ring), y-tocotrienol, also with a mass of 410 (like (3-tocotrienol but with loss of a different methyl group on the phenyl ring) and 8-tocotrienol with a mass of 396 (like (3-tocotrienol but with the loss of two methyl groups from the phenyl ring). 

Shown in Figure 4 is the photodissociation of protonated N,N -bis(4,6-dimethoxysalicylidene)-4-trifluoromethyl-o-phenylenediimin-ato cobalt (II) (CoSALOPH), which is also produced by ion/molecule reactions of electron impact fragments with the neutral molecule. This ion dissociated by loss of a methyl group (Equation 2). 

No metastable peak has been observed for loss of a methyl group following El of acetaldehyde, CH3CHO however, the metastable ion decomposition to lose CD3 has been seen with CD3CDO [695], This intermolecular isotope effect has been interpreted in terms of the isomerisation (CH3CHO)f - (CH2=CHOH)t occurring in the unlabelled molecule and precluding methyl loss [695]. 

McLafferty Rearrangement of Ketones and Aldehydes The mass spectrum of butyraldehyde (Figure 18-4) shows the peaks we expect at m/z 72 (molecular ion), m/z 57 (loss of a methyl group), and m/z 29 (loss of a propyl group). The peak at m/z 57 is from cleavage between the /3 and y carbons to give a resonance-stabilized carbocation. This is also a common fragmentation with carbonyl compounds like the other odd-numbered peaks, it results from loss of a radical. 

The base peak in the mass spectrum occurs at m/z = 55. This peak represents loss of a methyl group from the molecular ion and indicates the presence of a methyl group in the unknown hydrocarbon. All other peaks occur with low intensity. 

Azines derived by double condensation of acetylpyridines with hydra-zene, decompose primarily by loss of a methyl group in a mass spectrometer. ) On thermolysis these materials gave complex and more or less intractable tars which would be consistent with decomposition occiming by a similar path. 

The mass spectra of S-alkylated thiophenium salts show a characteristic loss of the alkyl group from sulfur, with the result that the spectra appear similar to those of the parent thiophenes. Masses higher than those observed for the parent thiophene rarely corresponded to a molecular ion. In such cases, loss of a hydrogen atom occurred in both methyl and ethyl salts to give an [M — 1] peak, which (when observable) was only of low intensity. Two structures, 4 or 5 have been proposed for this ion. In the case of the S-ethyl salts, further loss of a methyl group may give rise to an [M — 16] " peak and the thiapyrylium structure (6) has been advanced for this species. 

---