Coupling constants aldehydes

The coupling constant of the aldehyde doublet 7.8 Hz) is repeated in the doublet of doublets signal at Sh = 6.3. Its larger splitting of 15.6 Hz is observed also in the doublet at Sh = 7.3 and indicates a CC double bond with a trans configuration of the vicinal protons. 

First the trans configuration of the C-2-C-3 double bond is derived from the large coupling constant Jhh = 15 Hz) of the protons at % = 5.10 and 7.11, whereby the middle CH proton (Sh = 5.10) appears as a doublet of doublets on account of the additional coupling ([Pg.189]

The ]H NMR spectrum shown is that of a compound isomeric with the one in Problem 19.65. This isomer has an IR absorption at 1730 cm-1. Propose a structure. [Note-. Aldehyde protons (CHO) often show low coupling constants to adjacent hydrogens, so the splitting of aldehyde signals is not always apparent.]... 

High-resolution H-NMR analysis has recently been employed to ascertain the nature and levels of aldehydes arising from the peroxidation of PUFAs. Indeed, chemical shifts, coupling patterns and coupling constants of the aldehydic (-CHO) and, for a,0-unsaturated... 

Typical proton and carbon chemical shift and coupling constant data for a-fluoroketones and aldehydes are given in Scheme 3.32, with data for esters being given in Scheme 3.33. 

Finally, a brief word about aldehydes. They are included at the end of this group for convenience only and should be spotted easily. Aldehydes bound to aromatic rings give sharp singlets at 10.2-9.9 ppm, whilst in alkyl systems, they give sharp signals at 10.0-9.7 ppm, which couple to adjacent alkyl protons with a relatively small coupling constants (2-4 Hz). 

It appears that, as the length of the chain of the aldehydo form increases, the extent of hydration decreases. For glyceraldehyde, the aldehydrol aldehyde ratio23 in deuterium oxide at 24° is 17.5 1 for d-erythrose it is 10 1. For the tetraacetate of aMehydo-L-arabinose in 7 3 oxolane-deuterium oxide, the ratio is 9 1 whereas, for the corresponding L-fucose derivative, which differs only in the presence of an additional carbon atom at the other end of the chain, it is 3 1. The chemical shifts and the coupling constants indicate that these two compounds, surprisingly, adopt different conformations.80... 

In the Horner-Emmons reaction (Scheme 3), the sulfonylphosphonate carbanion 5 is formed in the presence of NaH and then reacts with an aldehyde to produce the intermediate 6 that undergoes in situ elimination to yield the vinyl sulfones and phosphonate anion. The sulfonyl group can stabilize the anion in the sulfonylphosphonate 5. The vinyl sulfones that are produced by this method using aldehydes as starting materials are exclusively the E (trans) isomers. The E-isomers of the vinyl sulfones are shown in the NMR spectra based on the coupling constants of the vinylic protons. Although strongly basic conditions are used in the Horner-Emmons reaction and a-amino aldehydes are easily racemized, the amino acid vinyl sulfones prepared by this method still show substantial optical activity. However, the enantiomeric purity of these compounds has not been determined. 5 ... 

We added the acetylene to aldehyde 12 now because this step is not compatible with a protected guanidine. Treatment of 43 with EtMgBr to form the acetylide and addition of aldehyde 12 afforded 54% of 45 and 32% of 44. Under the basic conditions, the secondary amine adds to the carbamate to form the oxazolidinone ring. The decrease in the geminal coupling constant of the methylene hydrogens adjacent to the nitrogen from 11 Hz in 43 to 8 Hz in oxazolidinone 45 is characteristic of the... 

Other examples of the application of calculations of spin-spin coupling constants by means of the PCM/DFT model for chemical problems using the IEF-PCM approach are studies of the spin-spin coupling constants in the keto and enol forms of monosubstituted 2-OH-pyridines [83], of the anomeric effect on the 27HH and 37HH coupling constants in 2-methylthiirane and 2-methyloxirane [83], and of the conformation of pyridine aldehyde derivaties [84], In these studies, PCM has been used to obtain a more realistic... 

Figure 18-1 shows the proton NMR spectrum of butanal. The aldehyde proton appears at 8 9.75, split by the protons on the a carbon atom with a small (/ = 1 Hz) coupling constant. The a protons appear at 8 2.4, and the /3 and y protons appear at increasing magnetic fields, as they are located farther from the deshielding effects of the carbonyl group. 

For 3-bromothiophene-2-aIdehyde (56), a long-range coupling-constant of 0.051 Hz was measured between H-4 and the aldehyde proton.175 From the peak widths of the / spectra, the value of T2 for the aldehyde proton was found to be 11.2 sec. Partial J spectra were obtained for this proton, and also for the ring protons of methyl furoate (57), by restricting the range of modulation frequencies... 

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