Couple of examples for judging 13C chemical shifts

Here are a couple of examples for judging ¹³C chemical shifts:

Remember that ¹³C shifts generally follow the pattern of ¹H shifts, but are much larger.
Thus, in (a)

• The peak at lowest field is the caarbon with the OH attached
• The peak at highest field is the CH₃ farthest from the OH
• Generally in both ¹³C and ¹H spectra, CH₂ groups fall to lower field than CH₃, which assigns the remaining peaks.

For (b):

• The peak at lowest field is the C=O carbon, shifted by electronegativity and "diamagnetic anisotropy"
• Assignment of the other two peaks follows from the CH₂ lower than CH₃ rule.

Now try predicting the splitting pattern to be found if the decoupler is turned off. 








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Isopropyl (1-methylethyl) group, with an extremely characteristic pattern

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The second spectrum illustrates several spectral features, including the unusual chemical shift of the aromatic hydrogen and an aldehyde H, and another characteristic alkyl splitting pattern.

The homotopic methyls at (a) and the unique H at (b) form an isopropyl (1-methylethyl) group, with an extremely characteristic pattern: doublet + septet, 6 : 1 integration ratio. As is often the case, we must expand the septet region to be able to see all seven peaks; if such an expansion is not available, the absorption may be referred to as a "multiplet", meaning "There's a bunch of lines there, but I can't quite count 'em!"
The pattern of the hydrogens on the benzene ring, (c) and (d), is also typical - typical for a 1,4-disubstituted benzene (para-disubstituted) with groups that differ distinctly, so that the hydrogens next to one substituent are in a significantly different environment than those next to the other. The two widely separated doublets (one neighbor) show clearly in the expansion.
The benzene chemical shift arises from an induced circulation of electrons:

The aldehyde H in R-CHO is usually found shifted downfield to the neighborhood of 9.5 ppm by an induced circulation of the p-electrons of the C=O. In Ar-CHO the additional circulation of the p-electrons of the benzene ring produces a further shift, to the vicinity of 10 ppm.










Tashkent, Uzbekistan

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en.wikipedia.org/wiki/Tashkent

Jump to Capital of Uzbekistan - [edit]. Independence Square. Tashkent is the capital of and the most cosmopolitan city in Uzbekistan. It was noted for its ...‎Tashkent International Airport - ‎Maksim Shatskikh - ‎Tashkent Metro - ‎


















 

 

 
 

 


 


 

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¹H and ¹³C NMR spectra of the abcc-monomer and the ABCC-sequence-regulated copolymer.

From Sequence-regulated vinyl copolymers by metal-catalysed step-growth radical polymerization

• Kotaro Satoh,
• Satoshi Ozawa,
• Masato Mizutani,
• Kanji Nagai
• & Masami Kamigaito

Nature Communications

1,Article number:6

doi:10.1038/ncomms1004

 a) ¹H and ¹³C NMR spectra of 7. (b) ¹H and ¹³C NMR spectra of poly(7) obtained with CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) ([CuCl]₀=200 mM; [PMDETA]₀=800 mM) in bulk at 100 °C. All spectra were measured in CDCl₃ at room temperature The brackets for repeating units in poly(7) are positioned differently from those in Figs. 1 and 4 so that the signals originating from the terminal groups can be assigned to the chemical structures.

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Ahmednagar,  Maharashtra, India

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  Ahmednagar is a medieval city. Numerous Mughal-era buildings dot the environs.Ahmednagar Fort, once considered the second most impregnable fort in India, …
  

  ‎Ahmednagar district - ‎Ahmednagar Fort - ‎History - ‎Mayor of Ahmednagar

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