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Friday, 20 October 2017

Ethyl acetate

Ethyl acetate example:

EthylacetateH

Predictions:
PositionIntegrationSplittingChemical Shift
12Three nearest neighbours that are equivalent – quartetSingle bond to oxygen – deshielded
23Two nearest neighbours that are equivalent – tripletSaturated alkyl group far from ester group – shielded
2′3No nearest neighbours – singletAdjacent to the carbon of a carbonyl – slightly deshielded

Ethyl crotonate

ehtylcrotonateblog1



Homonuclear J-resolved Spectroscopy (JRES): An Educational Tool


Many undergraduates that have been introduced to NMR understand the concepts of chemical shift and coupling, however struggle when presented with a real 1H NMR spectrum. For a novice at interpreting proton NMR spectra, it can be difficult to distinguish between separate resonances and multiplets belonging to the same resonance.
‘JRES’ is a 2D homonuclear experiment that produces a J-resolved spectrum, i.e. the chemical shift along one axis (f2) and the proton-proton coupling along the other axis (f1). Essentially, the projection along f2 is a decoupled proton spectrum, which greatly simplifies the spectrum and allows students to quickly identify the chemical shift and coupling pattern.
Comparison of the JRES spectrum with the 1D proton spectrum allows students to understand how proton-proton coupling affects the appearance of the spectrum and become more confident at distinguishing between multiplets and different resonances.



ehtylcrotonateblog2

In the 1D proton NMR spectrum there are a set of peaks around 5.5-6 ppm. It is not obvious to the beginner whether these are two separate resonances or a large doublet. In the JRES we can see that in fact the two resonances collapse into one peak in the f2 dimension and is split into a doublet in the f1 dimension, which means the peaks are one proton split into a doublet. From the 1D proton spectrum it is also difficult to determine whether the set of peaks between 6.3-7.2 ppm is one or multiple resonances, and what the splitting pattern is. This is resolved in the JRES spectrum where again all of the peaks collapse into one in the f2 dimension, so the set of peaks is due to one resonance. It can also be determined by JRES that it is split into a doublet of quartets, which is difficult to see in the 1D proton NMR spectrum.




NMR EXAMPLES

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  • Figure 1Proton NMR of 100% Methyl Acetate


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 2Proton NMR of 100% Methyl Propionate







Proton NMR of 100% Methyl Butyrate






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1H NMR spectra of the C4H8O2 isomers

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Ethyl(1R,2S,3S,4S)-2-(furan-2-yl)-3-nitro-6-oxobicyclo[2.2.2]octane-1-carboxylate



Ethyl(1R,2S,3S,4S)-2-(furan-2-yl)-3-nitro-6-oxobicyclo[2.2.2]octane-1-carboxylate


Compound 7 Ethyl(1R,2S,3S,4S)-2-(furan-2-yl)-3-nitro-6-oxobicyclo[2.2.2]octane-1-carboxylate To a solution of CAT 10 (128 mg, 0.37 mmol) and the nitroolefin 9 (3.1 g, 22.3 mmol) in 10 mL anhydrous CH2Cl2 at room temperature was added enone 8 (1.8 g, 10.7 mmol). The resulting mixture was stirred at the same temperature until enone 8 is consumed as indicated by TLC. Then DBU (0.34 mL, 3.20 mmol) was added and the mixture was allowed to stir at ambient temperature until completion as indicated by TLC. The solution was concentrated in vacuo and purified by flash chromatography on silica gel (Hexane / EtOAc = 20 / 1) to give 7 (2 g, 61% yield) as a yellow solid. [α]D 23 28.0 (c = 1.0, CHCl3).

1H NMR (400 MHz, CDCl3): δ 7.29 (d, J = 0.8 Hz, 1H), 6.27 (dd, J = 2.0 Hz, J = 3.2 Hz, 1H), 6.14 (d, J = 4.0 Hz, 1H), 4.93 (m, 1H), 4.57 (d, J = 4.4 Hz, 1H), 4.11 (m, 2H), 3.04-3.02 (m, 1H), 2.80-2.75 (m, 1H), 2.60- 2.54 (m, 1H), 2.33-2.29 (m, 1H), 1.88-1.72 (m, 2H), 1.33-1.23 (m, 1H), 1.21 (t, J = 7.2 Hz, 3H).

13C NMR (100 MHz, CDCl3): δ 204.1, 168.7, 151.8, 142.5, 110.5, 108.1, 88.3, 61.3, 56.3, 42.0, 40.8, 33.7, 26.9, 19.2, 13.8.

IR (thin film): 3435, 3141, 3120, 2996, 2959, 1715, 1653, 1621, 1557, 1505, 1473, 1443, 1408, 1371, 1336, 1301, 1336, 1301, 1270, 1236, 1142, 1120, 1083, 1062, 1074, 1045, 1045, 1011, 996, 960, 930, 892, 884, 867, 803, 753, 628, 600, 508, 436 cm-1 .

LRMS (ESI): 308.0 (M+H)+ , 330.0 (M+Na)+ .

 HRMS (ESI): calcd for C15H18O6N (M+H) + : 308.1129. Found: 308.1130.

 Melting point: 117-118 oC.



Concise asymmetric total synthesis of (−)-patchouli alcohol


 Author affiliations

Abstract

The asymmetric total synthesis of (−)-patchouli alcohol was accomplished in a concise manner. Key reactions include a highly diastereo- and enantioselective formal organocatalytic [4 + 2] cycloaddition reaction, a radical denitration reaction, and an oxidative carboxylation reaction. The formal synthesis of norpatchoulenol was achieved as well.
Graphical abstract: Concise asymmetric total synthesis of (−)-patchouli alcohol


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Thursday, 19 October 2017

2-Methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline

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Two-dimensional proton–proton NMR correlation spectrum of 2-methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline in acetone-d6. A colour code was used to highlight the observed H–H couplings.



image file: c6ra20886j-s2.tif


Scheme 2 Pd-mediated hydrolysis of triethylamine in the presence of 2-tosylaminomethylaniline (HATs) to yield 2-methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline and di(acetato)bis(diethylamine)palladium(II).

2-Methyl-3-tosyl-1,2,3,4-tetrahydroquinazoline

Yield = 12.3 mg (41%). 1H NMR (400 MHz, dmso-d6): δ/ppm 7.56 (d, J = 8.2 Hz, 2H, 2 × H-2′), 7.16 (d, J = 8.1 Hz, 2H, 2 × H-3′), 6.83 (m, 2H, H-5 + H-7), 6.46 (t, J = 7.1, 1H, H-6), 6.25 (d, J = 8.1 Hz, 1H, H-8), 6.09 (d, J = 3.4 Hz, 1H, NH), 5.22 (m, 1H, H-2), 4.54 (d, J = 17.2 Hz, 1H, CHH-4) and 4.36 (d, J = 17.2 Hz, 1H, CHH-4), 2.25 (s, 3H, CH3-4′) and 1.22 (d, 3H, J = 6.3 Hz, CH3-2). 1H NMR (250 MHz, CDCl3): δ/ppm 7.59 (d, J = 8.3 Hz, 2H, 2 × H-2′), 7.06 (d, J = 8.3 Hz, 2H, 2 × H-3′), 6.90 (t, 1H, H-7), 6.86 (d, 1H, H-5), 6.67 (dt, J = 7.5 and 1.1 Hz, 1H, H-6), 6.29 (d, J = 8.1 Hz, 1H, H-8), 5.36 (dq, J = 6.4 and 1.0 Hz, 1H, H-2), 4.70 (d, J = 17.4 Hz, 1H, CH2-4), 4.47 (d, J = 17.4 Hz, 1H, CH2-4), 2.29 (s, 3H, CH3) and 1.40 (d, J = 6.4 Hz, 3H, CH3). 13C NMR (62.5 MHz, CDCl3): δ/ppm 143.2 (C4′), 139.7 (C8a), 136.2 (C1′), 129.0 (2 × C3′), 127.6 (C5), 127.3 (2 × C2′), 126.4 (C7), 118.8 (C6), 116.9 (C4a), 116.4 (C8), 61.4 (CH), 41.8 (CH2), 21.5 (CH3) and 21.4 (CH3). IR (KBr, cm−1): 3387(s) ν(NH) cm−1, 1326(s) νas(SO2), 1158(vs) νs(SO2). MS (ESI) m/z = 325 (MNa+). HRMS calcd for C16H18N2NaO2S (MNa+): 325.0981; found, 325.0967. Elemental analysis (found): C 63.5, H 5.8, N 9.1; S, 10.5%. Calc. for C16H18N2O2S: C, 63.6; H, 6.0; N, 9.3; S, 10.6%.




http://pubs.rsc.org/en/content/articlehtml/2016/RA/C6RA20886J


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NMR PRESENTATION


NMR PRESENTATION