-Need help with organic chemistry, NMR IR and Carbon 13 (tips and tricks to usin
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Question
-Need help with organic chemistry, NMR IR and Carbon 13 (tips and tricks to using them induvidually to find out the structure of the molecuel as well as together)!! ??
Synthesis: breakdown of a step by step process how to solve them?
Major Minor Structures?
Resonance structures, step by step process, (I am comfortble with the concepts! I just get carried away and am fuzzy on the overall objective of resodence structures so I find my self making 5 when I should have only made 2 or what not. aslo how to draw the proper hybrid resonance structure?
Transition State how to draw the actual transistion state molecule and what it means?
What is Syn and anti syn what is markinov and anti markinove?
Newman projection energy diagrams for looking from the C3-C4 and what does the C3 to C4 or C2 to C3 mean?
Tips on epoxides!!!!!!!!!!!!?
Reaction cordinates for the various mechanissms?
Explanation / Answer
Spectroscopy (NMR, IR)
When I solve problems involving spectra (mass spec, NMR, IR), I usually start with the mass spectrum in order to determine a molecular formula and the degrees of unsaturation (number of rings + pi bonds). If you're given the molecular formula, tha'ts even better--determine the dergees of unsaturation as soon as you can.
The next thing you should do is use the IR to determine what functional groups you have. Specifically, do you have a C=O? What kind of C-H bonds do you have? Is there an OH present? What about NH? Those are all questions an IR can answer with relative certainty.
The last thing you should do is look at the NMR. A proton NMR will give you the fine details of a structure, but it really helps to have some information from the mass spectrum (i.e. molecular formula) and the functional groups first. More importantly, you can discern other functional groups from the NMR based on the chemical shift values. For instance, you ought to know that the aromatic region is 6 - 8 ppm and is a fantastic way to discern whether or not a benzene ring is in your molecule.
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Synthesis problems are hard no matter what. You need to know your chemistry pretty thoroughly in order to do them quickly. The best, most systematic way to do them is to take your target compound and disconnect bonds one-by-one from the end. That is, to work backwards toward the starting material you're allowed to use.
Then use a forward synthesis (i.e. do the reactions fowards) in order to 'check' your work and see if it will make the desired target.
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Major/minor structures? I'm not sure what you mean. Are you talking about major / minor products? Usually these are from problems in which more than one product is possible, but one is preferred over another. For instance, recall that Zaitzev's rule states that the most substituted double bond is the most stable double bond. Thus, a major product will form the more substituted alkene. Minor products are possible when you CAN form them, but they're not the most stable product (for example, forming a di-substituted alkene when a tri-substituted alkene is possible).
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Resonance structures are ways to represent the distribution of electrons in a compound. The best resonance structures give all atoms their octet, have more bonds and less charge, etc. These are concepts with which you are no doubt familiar.
As far as where to stop, that's a tough question. You want to be in the habit of drawing the next best resonance structure, which follows the rules above. Drawing resonance structures which have too much charge are not good ones, and so you should not draw them.
Resonance hybrids can be drawn with these general rules in mind: if in all the major resonance structures an atom retained a lone pair, you should draw the lone pair on the atom in the hybrid. If there was a double bond between two atoms in one of the resonance structures, you should draw a partial double bond in the hybrid. If an atom had a charge in any one of the resonance structures, it takes on a partial charge of the same sign in the hybrid.
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The transition state of a molecule shows the moment the bonds break and form. Bonds breaking and forming are shown by dotted lines, and partial charges are also shown based on the changes in electron density. For instance, you would show a leaving group with a partial negative charge because it's gaining electrons (a full negative charge) in the products.
Transition states can't be isolated. They are the "point" where the bonds form and break in a reaction.
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Syn addition indicates that something is added across a doule bond from the SAME side. For example, when you add BH3/H2O2/NaOH to a double bond, the H and OH atoms that you get in your product are on the SAME side of the alkene.
Anti addition describes addition to a double bond that occurs from the opposite side of the double bond. Br2 and Cl2 are examples of anti addition.
Markinokov addition is where you add atoms across a double bond, for example, H and OH. In Markinokov addition, OH adds to the more substituted carbon (an example is adding H3O+ to an alkene).
In anti-Markinokov addition, if we use the same system of H and OH, the OH ends up on the less substituted carbon. (An example is hydroboration).
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In Newman projects, when we say C2 to C3, we are talking about carbon two and carbon three. Count the carbons and draw the newman project as if you're looking down the bond from carbon two to carbon three.
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Epoxides are kind of annoying to deal with at first. If you're in acidic conditions, you protonate the epoxide first and then open it from the more substituted carbon with your weak nucleophile.
If you're in basic conditions, you open the epoxide from the less substituted carbon.
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Keep in mind that SN2 and E2 reaction diagrams (the reaction coordinate diagrams) have one hump because they only have one transition state (the top of the hill). They are only ONE step.
On the other hand, SN1 and E1 mechanisms have two humps because they have two transitions states (The peaks of each hill). The intermediate is the bottom peak between the two hills. They are TWO step mechanisms.
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I hope this helps. Let me know if you've any questions.
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