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# 化学代写|有机化学代考Organic Chemistry代写|CHEM137 Solving for Unknown Structures Using Spectroscopy

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## 化学代写|有机化学代考Organic Chemistry代写|Solving for Unknown Structures Using Spectroscopy

1. Determine the degrees of unsaturation in the molecule to see how many rings or double bonds are present.

Use the following formula, where $C$ is the number of carbons and $H$ is the number of hydrogens:
$$\text { DOU }=(2 C+2-H) \div 2$$
Double bonds and rings count as one degree of unsaturation, and triple bonds count as two degrees. Remember the following conversions: Add $1 \mathrm{H}$ to the formula for halogens, subtract $1 \mathrm{H}$ from the formula for nitrogens, and ignore oxygens.

1. Look at the IR (if you’re given one) to see the major functional groups present in the molecule.
Chapter 15 discusses IR spectroscopy.
2. Determine from the integration how many hydrogens each peak represents, and use that information to determine the structure of all the fragments of the molecule.
Table 16-1 shows a list of the common fragments. (See the preceding section for info on finding the number of hydrogens each peak represents.)
Sum together all the atoms in your fragments to make certain that the sum of the atoms in the fragments matches the molecular formula (to make sure you’re not missing any atoms).
3. Put together the fragments of the molecule that makes sense with the chemical shift and coupling.

Generate all possible structures based on the fragments you found in Step 3. Remember that structures you propose almost always have no charges and that each atom obeys the octet rule.

1. Double check your proposed structure to ensure it makes sense with the chemical shifts, integration, and coupling.

Go back and predict what you think your proposed structure’s NMR spectrum would look like and see whether it matches the actual spectrum.

## 化学代写|有机化学代考Organic Chemistry代写|Thou Shalt Work the Practice Problems before Reading the Answers

Working the practice problems is the greatest commandment of all, so I put it first. Organic chem textbooks today weigh more than most small children, and practicing problems helps you remember the concepts for the long term. After you complete a problem and see where you made the mistakes and correct those mistakes, the ideas become engrained into your bones.

Reading the material is a good idea, but after a while, your brain reservoir fills and all the info that follows starts pouring over the dam. You soon forget any material you haven’t practiced. That’s a problem, because organic chemistry builds on itself, using information that’s taught at the beginning of the course as a foundation for the new material. It’s not like a history class, where if you didn’t understand the culture of Australopithecus, you can still figure out the ancient Romans.

In organic chemistry, if you don’t understand the basics of bonding, for example, then you’re really sandbagged when you get to reactions, because the text and practice problems assume that you understand bonding. Of course, you can prevent all this trouble by working the problems.

Unfortunately, one of the most common ways that students “practice problems” is by reading the solutions manual. Similarly, I tried to “practice piano” by listening to concertos. That didn’t work out for me, I’m afraid, and for those of you who work problems by reading the solutions guide – well, let me just suggest that it won’t work out too well for you, either. Regrettably, there’s no substitute for a few hours spent with the pencil, taking the time to honestly work the problems. In this class, lazy students lose, and the students who work hard (like you) win.

## 化学代写|有机化学代考Organic Chemistry代写|Solving for Unknown Structures Using Spectroscopy

$$\mathrm{DOU}=(2 C+2-H) \div 2$$

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