OChem 2 Lecture
OChem 2 Lecture CHEM 30133
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This 2 page Study Guide was uploaded by Veronica Morgan on Sunday February 28, 2016. The Study Guide belongs to CHEM 30133 at Texas Christian University taught by Dr. Dzyuba in Spring 2016. Since its upload, it has received 51 views. For similar materials see Organic Chemistry 2 in Organic Chemistry at Texas Christian University.
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Date Created: 02/28/16
Ochem Exam 2 Study Guide Rho value tells how big the charge in the transition sate is If you chart rho, electron donating groups will have a negative value, and electron withdrawing groups will have a positive rho value Rate of the reaction = rho times sigma If there is a negative transition state, there will be a positive rho value which means the electron withdrawing group stabilizes because there is an increased negative charge for the reaction Localized charge increases reactivity which means less stable and less acidic group (localized is there is an electron donating group) Delocalized charge decreases reactivity which means a more stable and more acidic group (delocalized is there is an electron withdrawing group) Sterics can mess up rho value Kinetic Isotope Effect Primary KIE is the reaction breaks the CH bond Value will be 67 Example is E2, ElCB irreversible, ElCB allylic Normal secondary KIE is when the carbon goes from sp3 to sp2 conformation Value is 1.11.4 Example is Sn2, Sn1, E1 Inverse secondary KIE is when the carbon goes from sp2 to 2p3 conformation Value is .8.9 Example is Sn2, Sn1, E1 Sn2 Sn1 Negative transition state Positive transition state Positive rho value Negative rho value Electron withdrawing groups are better Electron donating groups are better Increase in negative charge Stabilized Positive charge with an electron withdrawing group increases size Positive charge with an electron donating group decreases size Negative charge with an electron withdrawing group decreases size Negative charge with an electron donating group increases size Electron donating group will increase pKa Electron withdrawing group will decrease pKa A bigger atom will be more basic R effect is weaker than I effect because of pi bonds +R effect, less acidic R effect, more acidic +I effect, less acidic I effect, more acidic Type Characteristics Example Soft acids low electronegativity, large Cu+, Ag+, I, Ch2 size, low charge Soft bases low electronegativity, large Alkenes, R2S, H, RSI size, high charge Hard acids High electronegativity, Co2, Fe3+, small size, high charge Hard bases High electronegativity, OH, F, Nr3 small size, high charge Examples of Good answers Water solvates charge better than EtOH hence charge is down and smaller charge will have a smaller rho value Sterics interfere so they rotate the bond and affect it Stronger +R so electrons are less available and less basic Better stabilized conjugate base so more acidic Delocalize charged so the rate is lower
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