study guide for exam 2
study guide for exam 2 CHEM 30133
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This 6 page Study Guide was uploaded by Veronica Morgan on Thursday March 10, 2016. The Study Guide belongs to CHEM 30133 at Texas Christian University taught by Dr. Minter in Fall 2016. Since its upload, it has received 34 views. For similar materials see Organic Chemistry 2 in Organic Chemistry at Texas Christian University.
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Date Created: 03/10/16
Ochem exam 2 study guide E1 mechanism Secondary KIE Rate determining step is formation of carbocation by LG leaving Tertiary works the best E2 mechanism Primary KIE Concerted reaction RDS is base attacking hydrogen Zaitsev product is more subsititued Hoffman product is less substituted Zaitsev will outnumber Hoffman unless the base is big and bulky Always has to be anti Syn occurs when E2 not possible E1CB Primary KIE in most basic sense however multiple types of ElCB RDS is formation of double bond after LG leaves Can be reversible or irreversible Can have ion pairs or be allylic SN1 Formation of carbocation is RDS Cis or trans Nucleophile prefer to attack the less hindered side by 5% SN2 Concerted Always leads to inversion of configuration Proved with isotopes Primary is best *tBuO can act as nucleophile or base* *watch for sterics in the reactions, sometimes cant be Sn1 or Sn2 if a certain shape* Ring opening of Epoxides Nucleophile always means reaction is basic If acidic conditions then expect a mixture of outcomes Electrophilic Aromatic Substitution Aromatic ring is nucleophile If EDG on ring, then reaction creates ortho and para products If EWG on ring, then reaction creates meta product because its better to have the electron deficient center away from the EWG Ipso substitution On same carbon as LG SiMe3 is a good Lg because its large and can delocalize charge well Ortho product doesn’t create because then you have to kick off H+ to reestablish aromaticity and you cant create a strong acid from a weaker acid Can use ipso substitution to create diazonium salt using HCL, NaNO2 and 0degreesC Diazonium Salt Reactions 1. Create sulfide 2. Create benzene 3. Create iodobenzene 4. Create phenol 5. Create nitrile 6. Create bromobenzene uses SRN1 (substitution reaction nucleophilic 1 species generated) for creation of bromobenzene, iodobenzene, and sulfide Nucleophilic Aromatic Substitution Aromatic ring is electrophile Need a good EWG to occur (cyano or MeF3) Good bases are OH, OMe, OEt, OnPr Attatck of 1,3 disubsitutued benzene leads to one product (meta) if R is EWG or three products (para, meta, and ortho with a 1:2:1 ration) if R is neutral like Me Attack of 1,4 disubstituted benzene leads to 50/50 mix of para and meta because R group is too far from LG to affect it Different Reactions Discussed in class 1. Addition of Br2 to a double bond creates trans dibromo alkane with a linear system it can be cis or trans with an aromatic system its just trans because of structure 2. if there is a solvent with addition of Br2, expect different products with combinations of Br and solvent because solvent occurs in great quantities 3. addition of Br2 to alkyne creates a trans dibromo alkene 4. if there is a solvent with the addition of Br2 (such as AcOH) then expect different products incorporating Br and OAc 5. addition of Br2 to diene will create a thermo product and a kinetic product 6. addition of Br2 with a radical can create three different structures depending on the conditions, 1bromocyclohexane, 3,bromo1cyclohexene, 1,2 dibromocyclohexane 7. reagent NBS = Br2 in small quantities so Br will be added on to part of the double bond usually with part of the solvent 8. AlBN over heat will attach whatever reagent there is to the reactant using a radical mechanism 9. R3SnH means a radical dehalogenation 10. BartonMcombie Deoxygenation replaces OH with H uses PhOSCl or NaH, CS2, MeI and Bu3SnH, AlBN, heat 11. H+/H20 usually means hydration of a double bond 12. Hg(OAc)2 over NaBH4 will act the same as H+/H2O 13. BH3 and NaOH/H202 will also hydrate double bond 14. RCO3H means epoxidation of double bond 15. 1)TsCL/base 2)nucleophile means inversion of stereochemistry: converts bad LG to good LG and inverts the stereochemistry 16. Mitsonobu Reaction uses DEAD Ochem Exam 1 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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