[hobomojo]

Sorry, there's so much to read. Where can I find practice tests with answers for Organic Chemistry 1 or anything that can help me with following topics? I'm using the book Organic Chemistry 6e by John Mcmurry, if that's vital information. My questions for specific topics are in red. I put some topics that I understand, mainly for references that you may have for where I can find practice. The topics that I state, I don't understand, don't necessary need input on because I know that's a lot to ask but if you're nice enough I'd appreciate it, mainly looking any good links to help me on those. Thanks in advance times a million!!!

Chapter 6 Alkenes: Structure and Stability

• Naming Alkenes
• Electronic Structure of Alkenes
• Cis-Trans Isomerism(1. I sort of understand how it works but when do I know when to add it to the name, is it always necessary?)
• Sequence Rules: The E,Z Designation(2. I understand for the most part but I don't get how to name the more complex ones with numbers placed in front of E or Z.Explain?)
• Stability Rules for Alkenes(3. How do I Calculate this?)
• Electrophilic addition of HX to Alkenes(I don't understand it at all)
• Markovnikov's Rule(4. I sort of understand it but what does the Major and Minor product mean? To make sure I understand, is it because the H will attach to the C with more substituents and the X(The Halide) will attach to the C with less substituents for the major product and then the vice-versa for the minor product. Also, the double bond breaks because so it can form a bond with H and Br, because if it didn't, then it would break the octet,is all this correct?) ? See the picture of the reaction at the bottom of the page.)
• Carbocation Stability(5. So, how do I tell which Carbocation is more stable?Is it the more Alkyl groups attached,then the more stable it is?)
• Hammond's Postulate(I don't understand at all)
• Electrophilic Addition:Carbocation Rearrangements(6. Are these just following Markovnikov's Rules)
• Hyperconjugation(7. I don't understand what Pi or Sigma bonds are, maybe explain them or reference a good page to help?) .

Chapter 7 Alkenes: Reactions and Stability
*Important Reactions to know*

• Dehydrohalogenation
• Dehydration
• Halogenation
• Halohydrin Formation
• Oxymercuration
• Hydroboration
• Acid-Catalyzed Hydration
• Addition of Carbenes
• Hydrogenation
• Oxidation of Alkenes

---------*Oxidative Cleavage of Double Bonds*
-------------A.Internal Bond
-------------B.Terminal Double Bond

9. What reactions follow Markovnikov's Rule? Which follow Anti-Markovnikov's Rules rule?

10. I greatly need help with understanding how to tell which reaction is which, how to predict what products are formed when given just the reactants, or what and why. Any tips on any on them would be great. If you know a good site to practice from or explains them, please do tell!

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[MissPhosgene]

Here is a link which may be helpful with each topic:

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/intro1.htm

Chapter 6: When an alkene can be either cis of trans, determine which one it is and use that in the name. Exception: rings which are smaller than 8 carbons. They are always cis and therefore the name is not necessary. For example: cyclooctene can have a cis or trans double bond and it is named accordingly. Cyclohexene is always cis and the isomerism at the double bond is not specified in the name. However, that only goes for alkenes fully in a ring. Exocyclic gets named.

Number the carbon at the beginning of the double bond. For example, take H3CCH2CH2C(H)=C(H)CH3

if the olefin were trans what would the name be? (E)-2-hexene. Cis: (Z)-2-hexene. Do you need to know the new way of naming?

Try reading this: http://research.cm.utexas.edu/nbauld/teach/alkenes1.html#nomen

To name alkenes, use regular naming rules such as finding the longest parent chain and name it according to the rules. Nothing changes except you have to add information abut the stereochemistry at the alkene.

Alkene stability: The more substituents bound to the alkene, the more stable. Trans is more stable than cis. Do you know why? It's probably explained in the book. There is a combination of two factors: hyperconjugation and bond strength. Hydrogen substituents directly bound to the alkene can't participate in hyperconjugation, a stabilizing interaction. Can you explain what hyperconjugation is and draw a picture which shows why a hydrogen can't hyperconjugate with an alkene but a methyl substituent can? Relative bond strengths are other factor. What is stronger: sp3-sp3 bond of sp2-sp3?

 You can calculate  :delta:H(hydrogenation) by using Hess' Law for the reaction going from alkene to alkane. (Enthalpy of formation of products minus enthalpy of formation of reactants).

Carbocation stability: Yes, the more carbon substituents, the more stable. Why? (Hint: think about why alkenes gain stability with increasing substitution) Also, what about carbanions and radicals?

Hammond postulate: in short, endothermic reaction: transition state resembles products. Exothermic reaction, transition states resemble starting materials. The TS has a free energy and so do the starting materials and the products. If the difference in free energy between the starting material and TS is smallest (exothermic), the TS resembles starting material. When the difference in free energy between the TS and product is smallest (endothermic), the TS resembles products.  Do you know why the difference in free energy between the starting material and products is smaller than the difference for the TS and products for an exothermic reaction? Can you explain Why the TS is closer in energy to the products compared to the starting material for an endothermic reaction? If not, try drawing reaction coordinate diagrams for each type of reaction.

Carbocation rearrangements are determined by carbocation stability. 3>2>1.  What do you think for a carbocation generated by dehydration of an alcohol with H2SO4? What about from 2-methylpropene when it is exposed to HBr? What is the basis for why Markovnikov's rule works?

Pi bonds: form between p orbitals. Electron density is above and below the bonding axis. As a result, they are weaker then sigma bonds. The areas of highest electron density are more "exposed" than for sigma bonds.

Sigma bonds: overlap between orbitals such that the electrons are more of less directly between the two nuclei. These are more directional. As a result of the location of the center of greatest electron density and the good overlap, these bonds are much stronger than pi bonds.

Try looking at wikipedia for pi and sigma bonds. If that doesn't help much, try

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Sigma-and-Pi-Bonds-858.html

http://www.chemguide.co.uk/atoms/bondingmenu.html#top

Look in the book for reactions which follow Markovnikov's rules. It will be very helpful for you to know why particular reagents give Markovnikov products and why other reagents give anti-Markovnikov products. How is hydroboration-oxidation different from addition of H-X?

For your final question: try drawing the arrow pushing for the addition of HBr to an alkene. Do it for each product. Pay attention to carbocation stability when you draw the arrow going from the alkene to H+.

The best thing to do is to learn mechanisms. If you can get the reasoning down regarding why a reaction occurs in the fashion it does, ochem will be much easier. I think ochem is taught a little differently from place to place, so maybe the best option is to ask your prof for exams given previously? Are there TAs available for you to talk with? Have you done all the problems out of the book for the chapters you have covered?

Try this if you want. Warning: when I clicked on the link, some terrible music started playing.

http://www.organicchemistryreview.com/


Electrophilic additions of H-X to alkenes: protonate in the place which results in the most stable carbocation. The major product will be the result of X- attacking the most stable carbocation. Your picture is correct, but when you wrote out a description under chapter 6 heading, what you said was the opposite. 

Electrophilic 1,2-addition v.s. 1,4-additions to conjugated dienes: what is the kinetic product and what is the thermodynamic product. Why?

Happy to answer/clarify any further questions.