Lecture 14: October 4, 2018

Transcription

1 CM 223 Organic Chemistry I Prof. Chad Landrie C 3 Ea + O 3 C O 2 reactant intermediate Lecture 14: October 4, 2018 Ch. 6: Section 6.8: Bond Dissociation Energies and Reaction Enthalpy Ch. 17: Sections: : Alcohols Ch. 10: Organohalides

2 CM 223 Organic Chemistry I Prof. Chad Landrie Ch. 10: Organohalides ( only) Ch. 17: Alcohols (17.1 & 17.2 only) Nomenclature of alides and Alcohols Sections: 10.1, 17.1

3 Functional Groups A functional group is a defined connectivity (constitution) for a specific group of atoms ( 2) within a molecule. Functional groups are responsible for a compounds physical and chemical properties, including its reactivity. alkene alkyne alcohol alkyl halide C C C C C C C C C O 3 C C O C X 3 C C X Slide 3

4 More Functional Groups A functional group is a defined connectivity (constitution) for a specific group of atoms ( 2) within a molecule. Functional groups are responsible for a compounds physical and chemical properties, including its reactivity. ether sulfide thiol amine C O C C S C C S C N C 3 C C 3 C O C3 3 C C C S 3 C C S 3 C C N Slide 4

5 3 C Carbonyl Functional Groups: Carboxylic Acid Derivatives carbonyl group O C pervasive common name O acetyl C 3 C acet- carboxylic acid ester acid halide amide O C O O C O 3 C O C O C O C C O 2 C 3 3 C O C X O C Cl 3 C Slide 5 O C N O C N acetic acid ethyl acetate acetyl chloride acetanilide Ph

6 Carbonyl Functional Groups carbonyl group O C aldehyde O pervasive common name O acetyl C 3 C acet- ketone O C C C C O O 3 C C 3 C C C3 acetaldehyde acetone Slide 6

7 Memorize These Functional Groups R = any carbon group many already encountered rewrite this table; use the minimum number of atoms required to define each functional group make flash cards you will be asked to identify and name functional groups on first exam Slide 7

8 IUPAC (Substitutive): Alkyl alides Br C 3 Br C C 3 C 2 CC 2 CC 2 C 3 3-bromo-5-methylheptane Steps: 1. Identify and number the longest continuous chain of carbons. 2. Follow all previous rules and conventions for naming/numbering alkane chains. 3. Name the compound according to the figure below. Conventions: Previous conventions apply (e.g., first point of difference rule). alogens and alkyl groups are considered to have equal rank when deciding numbering. If two numbering schemes give same locant, choose numbering that lists substituents alphabetically. Subsituent names for halogens are flouro, chloro, bromo, & iodo. parent locant halo substituent parent chain name Slide 8

9 4 Cl Cl 5 3 C 2 C 2 CC 3 O C CC 2 O 5-chloro-2,3-dimethylpent-1-ol or 5-chloro-2,3-dimethyl-1-pentanol Steps: 1. Identify and number the longest continuous chain of carbons to give the -O group the lowest locant. 2. Name the parent by replacing -e with -ol (e.g. pentane becomes pentanol). 3. Name the compound according to the figure below. Conventions: Previous conventions apply (e.g., first point of difference rule). Alcohols outrank (have priority over) halogens and alkyl groups when considering numbering scheme. Alcohol locant may be placed before the parent name (e.g. 1-pentanol) or after ( e.g. pent-1-ol). locant IUPAC (Substitutive): Alcohols parent (drop last e ) ol parent (drop last e ) locant ol Slide 9

10 Substitutive vs. Functional Class Nomenclature substitutive and 2004 name are preferred exams, quizzes, will only contain substitutive and 2004 names???? old habits are hard to break Slide 10

11 Classification of Substituted Carbons count the number of carbons bonded to the carbon atom you wish to classify: one = primary (1º) two = secondary (2º) three = tertiary (3º) four = quaternary (4º) Slide 11

12 i>clicker Question What is the IUPAC (2004) name for the following molecule? O Br A. 3-hydroxy-4,5,6-triethyl-7-bromooctane B. 2-bromo-3,4,5-triethyloctan-3-ol C. 7-bromo-4,5,6-triethyloctan-3-ol D. 4-(3-bromo-1,2-diethylbutyl)-3-hexanol E. 6-(1-bromoethyl)-4,5-diethyl-3-octanol Slide 12

13 CM 223 Organic Chemistry I Prof. Chad Landrie Properties of Alcohols and Alkyl alides Sections: 17.2, 10.1

14 Review: Boiling Points Increase with # of Carbons boiling point increases with increasing number of carbon atoms branched alkanes have lower boililng points than unbranched isomers Slide 14

15 Alcohols and Alkyl alides Are Polar red = higher electron density (partial negative charge) blue = lower/ deficient electron density (partial positive charge) Slide 15

16 Affect of Structure on Boiling Points only London dispersion forces aka: induceddipole/induced-dipole C3C2C3 (propane) induced/induced dipole-dipole attractive force dipole/induced-dipole C3C2F (fluoroethane) induced/induced dipole-dipole attractive force dipole/induced-dipole hydrogen bonding C3C2O (ethanol) MW boiling point (ºC) Dipole moment (D) Slide 16

17 Review: Induced-dipole/Induced-dipole (London Dispersion) C C C C C more atoms = more electrons = more induced dipoles = C C C C C more attractive forces = higher boiling point Slide 17

18 Dipole/Induced-Dipole C C F permanent dipole in one molecule induces a temporary dipole in a non-polar region of another molecule C C F more C-X bonds = more dipole/dipole-induced attractive forces Slide 18

19 Dipole/Dipole C C C C Cl Cl attractive force between two permanent dipoles not necessarily only at the polar covalent bond: region of partial positive charge in one molecule attracted to region of negative charge in another molecule. Slide 19

20 ydrogen Bonding is a Strong Dipole/Dipole Attractive Force Slide 20

21 Boiling Point Trends in same class (e.g., X=F) boiling point increases as MW increases; more atoms = more LDFs = higher boiling point alcohols have significantly higher boiling points than similar halides; strong hydrogen bonding attractive forces boiling point increases from fluorine to iodine for same series; polarizability of halogen increases down periodic table = greater LDFs Slide 21

22 Polarizability Polarizability is a measure of the ability of an external electric field to distort the electron cloud of a molecular entity; it s the flexibility, squishiness of the electron cloud; squishier clouds = greater induced-dipoles. bromomethane (bp = 3 ºC) fluoromethane (bp = -78 ºC) polarizability increases down the periodic table; larger orbitals; more polarizable = better able to momentarily generate induced-dipole = stronger induced-dipole/induceddipole forces = more attractive forces = higher boiling point Slide 22

23 Boiling Point Trends (Cl, Br, I Only) Boiling point increases with increasing number of halogens despite CCl4 having no molecular dipole, it has the highest boiling point induced-dipole/induced-dipole forces are the greatest because it has the greatest number of chlorine atoms Slide 23

24 Polarizability and Teflon Teflon = polytetrafluoroethylene (PTFE) F F F F F F F F F F F n F more bonds to F (low polarizability) = less/weaker induceddipole/induced-dipole attractive forces Slide 24

25 i>clicker Question Rank the following in order of increasing boiling point. a b c d lowest highest A. b < c < a < d B. c < a < d < b C. b < d < c < a D. c < a < b < d E. none of the above Slide 25

26 CM 223 Organic Chemistry I Prof. Chad Landrie Reaction Chemistry: Preparation of Alkyl alides Section: 6.8: Reaction Enthalpy, Bond Dissociation Energies and Rates of Reactions

27 Components of a Chemical Reaction 3 C O 2 SO 4, 2 O 3 C 100 ºC, 1 h reversible 3 C O Cl, C 2 Cl 2 40 ºC, 5 h irreversible 3 C Cl reagents such as catalysts, acid/bases, solvents are written above and below the reaction arrow conditions such as time and temp can be included above and below the reaction arrow reactions are written as either equilibria (reversible) or as non-equilibria (irreversible) Slide 27

28 Describing a Chemical Reaction Is the reaction fast or slow? Does the reaction release (exothermic) or absorb (endothermic) heat? Is the reaction spontaneous (exergonic) or non-spontaneous (endergonic)? Kinetics Determined by activation energy, Ea Thermodynamics Determined by reaction enthalpy, Spontaneity Determined by reaction Gibbs free energy, G Slide 28

29 Is the Reaction Exothermic or Endothermic reactants formation of stronger bonds products reactants IF S = 0, then: º < 0 (negative) Gº < 0 (negative) K > 1 products Bond Formation = releases heat Bond Cleavage/Breaking = absorb heat Exothermic reaction = the energy released by forming bonds is greater (stronger bonds) than the energy absorbed to break bonds (weaker) Energy required to break a bond is called bond dissociation energy (BDE) Slide 29

30 Is the Reaction Exothermic or Endothermic reactants formation of stronger bonds products Bond Dissociation Energy (BDE) Slide 30

31 Is the Reaction Exothermic or Endothermic reactants formation of weaker bonds products reactants products IF S = 0, then: º > 0 (negative) Gº > 0 (negative) K < 1 Bond Formation = releases heat Bond Cleavage/Breaking = absorb heat Endothermic reaction = the energy released by forming bonds is less than (weaker bonds) than the energy absorbed to break bonds (stronger) Energy required to break a bond is called bond dissociation energy (BDE) Slide 31

32 Is the Reaction Fast or Slow? 3 C δ + δ + O 2 Transition states cannot be isolated or measured. They are inferred. They involve partial bond cleavage and/or partial bond formation. transition state: energy maximum along reaction coordinate for one elementary step; usually involves partial bond making and partial bond breaking Ea C 3 + O activation energy: energy difference between the transition state and the reactant 3 C O 2 intermediate intermediate: energy minimum along the reaction coordinate; species with a finite lifetime; neither reactant, nor product reactant product ammond Postulate: structure of the transition state looks most like its closest energy reactant or intermediate Slide 32

33 Is the Reaction Fast or Slow? aa + bb cc The rate of the reaction depends on the concentration of the reactants as well as the size of the activation energy. Arrhenius Equation: Transition State Theory: Ea k = rate constant A = pre-exponential factor (reaction specific) Ea = activation energy R = gas constant T = temperature Slide 33

34 Is the Reaction Fast or Slow? aa + bb cc The rate of the reaction depends on the concentration of the reactants as well as the size of the activation energy. Arrhenius Equation: Transition State Theory: Ea total collisions per second propability a collision will result in a reaction number of collisions resulting in a reaction per second Slide 34

35 i>clicker Question What is the enthalpy of reaction for: BDE (KJ/mol) C C 369 C O 391 C 410 Cl 431 O 497 C Cl 354 A. -29 B. 37 C. -37 D. -66 E. 77 Slide 35

36 i>clicker Question When reactions are said to be reactive, that means that they undergo a chemical reaction relatively fast compared to one or more other chemical reactions. Which reaction coordinate diagram represents the most reactive reaction? A B C D Ea Slide 36

37 i>clicker Question Given the answer below, how could a particular reaction be made more reactive? A. Decrease the energy of the reactant. B. Decrease the energy of the product. C. Increase the energy of the transition state (TS). D. Decrease the energy of the TS and reactant. E. None of the above. Ea To decrease Ea you must raise the energy of the reactant and/or lower the energy of the TS. Slide 37

38 CM 223 Organic Chemistry I Prof. Chad Landrie Nulceophilic Substitution

39 i>clicker Question Today we will be discussing the substitution of alcohols by halides. Depending on the conditions and reactants, this reaction can be very slow like the one below. What changes would increase the rate of this reaction? Bond BDE (kj/mol) F 570 Br 366 Cl 431 O 497 C3C2 Cl 352 (C3)2C Cl 354 C3C2 F 525 C3C2 O 400 (C3)3C O 400 reactant Ea O + Cl Cl intermediate product + O A. Use a solvent that raises the energy of the transition state. B. Use F instead of Cl. C. Use an alcohol with a stronger C-O bond. D. Dilute the reaction with more solvent. E. Use Br instead of Cl Slide 39

40 Preparation of Alkyl alides By Substitution of Alcohols R O + X R X + O hydroxyl group alcohol halide hydrogen halide alkyl halide water ydroxyl group is being substituted (replaced with) a halide Slide 40

41 Review: Preparation of Alkyl alides By Substitution of Alcohols R O + X R X + O alcohol hydrogen halide alkyl halide water Increasing Reactivity 3º alcohol 2º alcohol 1º alcohol Reactivity describes the relative rate of two or more reactions. The rate of a reaction is controlled by the concentration of reactants, temperature and activation energy (Ea). Slide 41

42 Increasing Reactivity (for methyl and 1º alcohols) Review: Preparation of Alkyl alides By Substitution of Alcohols R O + X R X + O alcohol hydrogen halide alkyl halide water I Br Cl F Increasing Reactivity 3º alcohol 2º alcohol 1º alcohol 2º O + Br cyclohexanol 1º C 3 (C 2 ) 5 C 2 O + Br 1-heptanol 80 ºC 73% 120 ºC 73% Br + 2 O bromocylcohexane water C 3 (C 2 ) 5 C 2 Br + 2 O 1-bromoheptane water Slide 42

43 Preparation of Alkyl alides from Alcohols R O + X R X + O alcohol hydrogen halide alkyl halide water R = alkyl groups alkyl groups = (carbon group; alkane subsituent) irreversible reaction; no equilibrium here more reactive reactants = faster reaction Slide 43

44 Alternative Conditions A mixture of sodium bromide and sulfuric acid may be used in place of Br. reagents generally placed above/below rxn arrow inorganic products usually omitted (assumed) Slide 44

45 1º and 2º Alcohols Unreactive Toward Cl 3º alcohol 1º alcohol O no rxn + Cl X Cl + O Primary alcohols are the least reactive. Cl is less reactive than Br. Primary alcohols then do not react with Cl ow can we increase the reactivity of this reaction? Slide 45

46 1º and 2º Alcohols Unreactive Toward Cl Thionyl chloride converts alcohols to alkyl halides through a different mechanism than Cl, which proceeds through smaller activation energies. thionyl chloride O S Cl Cl SOCl2 O SOCl 2 + Cl Cl + SO 2 + Cl K 2 CO 3 thionyl chloride reacts rapidly with 1º and 2º alcohols byproducts of the reaction are SO2(g) and Cl(g) base is needed to neutralize Cl: e.g. K2CO3, pyridine Slide 46

47 i>clicker Question Predict the organic product of the following reaction. Br O 3 C C 3 Cl 25 ºC? Cl A B C O Br Cl Cl Cl 3 C C 3 3 C C 3 3 C C 3 D Br O Cl E Cl Cl 3 C C 3 Cl 3 C CCl 3 Slide 47

48 CM 223 Organic Chemistry I Prof. Chad Landrie Next Lecture ,

49 CM 223 Organic Chemistry I Prof. Chad Landrie Skillbuilder Three: NMR

50 Question One J = 7.1 z J = 7.1 z M.F.: C48O

51 Question Two Dissolves in NaO/2O 1 2 2

52 Question 3 MF: C

53 Question

54 Question 5 d MF: C611N t m 2 3 6

55 Question 6

56 Question 7 MF: C714O dt

57 Question 8 MF: C48Cl

58 Question aromatic -NO2: ~1550 and 1350 cm -1 alkyl -NO2: ~1580 and 1380 cm -1

59 Question 10 d (J = 6.16 z) MF: C819N m (J = 6.6 z) q (J = 7.1 z) t (J = 7.1 z)

60 Question 11