C-13 NMR or NMR in general

[Awuah29]

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Guys ,
I am looking for a post on NMR in general or CNMR that was posted . I read wikepedia and other sources , but doesn't make sense with the examples they gave. One example from Destroyer # 23 I believe

Which carbon would have the most downfield signal in C-13 ?
The answer is 23 B, the carbonyl.

Now I dont have to remember the ppm right? All I have to know is that carboxylic acids , aldehydes, aromatic, alkenes are downfield? Alkeynes , akyl , alkanes, are shielded and upfield. Please let me know and post a link cause i've been searching for examples.
thanks

 

[wifi08]

no u dont have to remember exact ppm but know whats more downfield than what

 

[klutzy1987]

The reason why in C13 a carbonyl is so far downfield is beacuse it has a double bonded O attached to it. The high electronegativity of O pushes it downfield somehow. The same would be in HNMR whatever is closest to a strongly electronegative element will be farthest downfield. Therefore Carboxy acids show up at 12.

 

[Awuah29]

The reason why in C13 a carbonyl is so far downfield is beacuse it has a double bonded O attached to it. The high electronegativity of O pushes it downfie somehow. The same would be in HNMR whatever is closest to a strongly electronegative element will be farthest downfield. Therefore Carboxy acids show up at 12.

thanks klutzy,
woah, what will I do without you East coast in the house!!!

 

[chessxwizard]

The resonance structure of a carbonyl makes it that much more downfield. Think about it... the carbon almost a cation, next to an electronegative oxygen!