Organic Reactions - Introduction to Organic Chemistry I | CHEM 231, Study notes of Organic Chemistry

Download Organic Reactions - Introduction to Organic Chemistry I | CHEM 231 and more Study notes Organic Chemistry in PDF only on Docsity! Chapter 5 - Overview of Organic Reactions* *Four major types of reactions… 1. Addition… Br2 Br Br + 2. Elimination… BrH base + "H-Br" CH3 CH3 OHI + OH - + I-3. Substitution… H+ 4. Rearrangement… *Two general kinds of bond breaking… C H homolytic homogenic C + H C I heterolytic heterogenic C + I nonpolar reaction polar reaction radical carbocation Step # 2 = two propagation steps (form C radicals) Step # 3 = three termination steps (remove components necessary for propagation) C+ Cl: : :2 ClCl Cl: : : CCl C2 C C Cl: : : CH Cl: : : H C radical, sp2 C ClCl C Cl + Cl: : : recycle to previous step C+ Question: What are the products of bromination of ethane? -> What radicals are formed? Regioselectivity of bromination >> greater than chlorination Relative rates of R-H substitution... X = Cl or Br R3CH R2CH2 RCH3 chlorination 5.2 3.9 1 bromination 1640 82 1 *Bond polarity (examples in Table 5.1)… C Z e- poor Z = O, N, halogens C Z e- rich Z = MgX, Li δ+ δ+δ−δ− ZC δ+ δ− Z = O, S, N Example # 2…alkene + HBr… Fact -> alkenes are more reactive that alkanes H H HH H Br CH3H H Br+ Br CH3 H Br H Br Br H H H H H H H H H H ::: : : : CH2H2C + H Br CH3CH2Br Keq *Rates & equilibria… Keq = CH3CH2Br CH2H2C HBr = 7.5 x 107 ∆Go = -RTlnKeq (R = 8.314 J/mol*K) Gibbs free energy change (E available to do work) ∆Go = Goproducts – Goreactants ∆Go < 0, Keq > 1 ∆Go = 0, Keq = 1 ∆Go > 0, Keq < 1 Basic equation: ∆Go = ∆Ho – T∆So ∆Ho = enthalpy change ∆So = entropy change For the above reaction at T = 298 K… ∆Go = -44.8 kJ/mol = -RTln(7.5 X 107) ∆Ho = -84.1 kJ/mol ∆So = -0.132 kJ/mol*K (T∆So = 39.3 kJ/mol)