Alkanes - Lecture Slides on Fundamentals of Organic Chemistry I | CHEM 3331, Study notes of Organic Chemistry

Download Alkanes - Lecture Slides on Fundamentals of Organic Chemistry I | CHEM 3331 and more Study notes Organic Chemistry in PDF only on Docsity! Chapter 3 1 Hydrocarbons - contain only C, H saturated - no C=C or C≡C unsaturated - contains one or more C=C or C≡C Saturated hydrocarbons - molecular formula = CnH2n+2 Chapter 3 2 A. Nomenclature 1. n-alkane names n = normal - straight chains CnH2n+2 or CH3-(CH2)n-2-CH3 n name structure bp (°C) 1 methane CH4 -164 2 ethane CH3CH3 -89 3 propane CH3CH2CH3 -42 4 butane CH3CH2CH2CH3 0 5 pentane CH3(CH2)3CH3 36 6 hexane CH3(CH2)4CH3 69 7 heptane CH3(CH2)5CH3 98 8 octane CH3(CH2)6CH3 126 9 nonane CH3(CH2)7CH3 151 10 decane CH3(CH2)8CH3 174 *memorize these Chapter 3 5 4. IUPAC Rules a. Find the longest continual chain of carbons - if two exist use the one with the largest number of groups (substituents). Chapter 3 6 b. Number the chain so the substituent positions are as low as possible and name each substiuent by its position number on the main chain. Chapter 3 7 c. When there are two or more substituents name them in alpha order and/or use the following, prefixes if they are the same: di -2 tri - 3 tetra - 4 penta - 5 hexa - 6, etc. Chapter 3 10 3. Rotation around C-C bonds: a. ethane - staggered = energy minimum eclipsed = energy maximum Chapter 3 11 b. propane - the barrier is raised a bit: Chapter 3 12 c. butane - there are two different C-C bonds to rotate around CH3CH2 CH2CH3 CH3 CH2CH2CH3 same as in propane a little more complicated Chapter 3 15 H3C H H H CH3 H trans-1,2-dimethylcyclopropane H3C H Cl H 12 3 cis- 1-chloro-3-methylcyclopentane 2. stability - ring strain needs to be minimized: a. get all angles as close to the ideal 109.5° as possible b. avoid eclipsing C-C and C-H bonds heat of combustion - gives relative energies (CH2)n + 3/2 nO2 nCO2 + nH2O + heat TABLE 3-4 Heats of Corrbustion (Per Mole) for Sore Simple Cycloalkanes Molar Heat Heat of Combustion Ring Strain Ring size Cyloalkane af Cambustion per CH, Group per CH, Group Tiatal Ring Strain 3 cyclopropane 400.8 keal 166.6 keal 9.2 keal 27.6 keal (115 KS) 4 cyclobulane 655.9 keal 164.0 keal 6.6 keal 264 keal (1 10K) 5 eyclopentane 793.5 keal 158.7 keal 1.3 keal 6.5 keal 27K) 6 cyclohexane S445 keal 157.4 keal 0.0 keal OO keal (OO KT) 7 evelohepline 1108.3 keal 158.3 keal 0.9 keal 6.3 keal (26 kI) 5 eyelooclane 1268.9 keal 158.6 keal 1.2 keal 9.6 keal (40 kK) relerenee: long-chain alkane 17.4 kcal 1.0 keal O.0 keal (0.0 kD) AHS kcal/mol : 29, BOS Ty OC (CHa), =i <2 166.3 163.9 158.7 157.4 157.5 158.3: 158.6 158.6 157.8 Chapter 3 17 3. cyclopropane H3C H3C H H H CH3 CH3 OO H3C O Pyrethin I - insecticide chrysanthemums Chapter 3 20 6. cyclohexane a near strain-free structure a. structure chair conformation: chair conformation of cyclohexane chair conformation H H Hon CHa \H We newnan projection "Aagpole" hydrogens boat conformation: boat conformation symmetrical boat of cyclohexane eclipsed am H (CH, HA H \ pons WOH Hy YH H H Newman projection “bwist” boat Chapter 3 22 NH2 CH H3C NH2 1-aminoadamantane rim antadine blocks association of influenza A with host cells • hallucinations • turning upside down Chapter 3 25 d. monosubstituted cyclohexanes Why is there an energy difference? TABLE 3-5 Energy Differences Between the Axial and Equatorial Conforrmations of Monosubstituted Cyelohexanes Eladall 2 Blequaterial x (keenleral | (iinet) oF a2 DB H 9 CN a2 0.8 gee 9 Cl as 21 a = 9 br 06 2.5 A = ia = 9 OH 1.0 4 —' equatorial § COOH La 59 x 8 CH, 7, 71 & CH.CH, 18 75 vodal 9 CHICH,) 21 38 § CICH,): 54 33 Chapter 3 26 e. di-substituted cyclohexanes 1,2- disubstituted R =~ R | ] ' R f ans AE=~19 R kcal/mol R : R ———— 3 R cis Chapter 3 27