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University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Prof. Duncan Wardrop October 8, 2012 CHEM 494 - Lecture 5.

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Presentation on theme: "University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Prof. Duncan Wardrop October 8, 2012 CHEM 494 - Lecture 5."— Presentation transcript:

1 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Prof. Duncan Wardrop October 8, 2012 CHEM Lecture 5

2 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Chapter 15 Alcohols and Alkyl Halides

3 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Functional Groups Alcohols and Alkyl Halides

4 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 Functional Groups functional group: a defined connectivity for a specific group of atoms (≥2) within a molecule since alkanes are chemically inert, functional groups are responsible for chemical reactivity under specific conditions and also the physical, chemical and biological properties of organic molecules b.p °C Inert to acids, bases, oxidizing & reducing agents b.p. = 78.4 °C Reacts with acids, bases, oxidizing & reducing agents Biologically Active!

5 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 5 Examples of Functional Groupsalkenealkynealcohol alkyl halide

6 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 6 Examples of Functional Groupsethersulfidethiolamine

7 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 7 Carbonyl Functional Groups: Carboxylic Acid Derivative carbonyl group pervasive common name carboxylic acid ester acid halide amide acetyl acet-

8 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 8 Carbonyl Functional Groupsketonealdehyde

9 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 9 Time to Memorize Functional Groups! many already encountered - alkenes, alkynes, arenes not alkanes study functional group handout from website - learn to draw & name F.G.s make flash cards you will be asked to identify and name functional groups on quiz 3 & first exam

10 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 10 IUPAC (Substitutive): Alkyl Halides 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). Halogens 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 fluoro, chloro, bromo, & iodo. 3-bromo-5-methylheptane parent locant halo substituent parent chain name

11 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 11 IUPAC (Substitutive): Alcohols Steps: 1.Identify and number the longest continuous chain of carbons to give the -OH 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). 5-chloro-2,3-dimethyl-pentan-1-ol locant“ol” parent (drop last “e”) 5-chloro-2,3-dimethyl-1-pentanol or locant“ol” parent (drop last “e”)

12 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 12 Two Substitutive Nomenclatures vs. Functional Group Class Nomenclature substitutive and 2004 name are preferred old habits are hard to break

13 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 13 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)

14 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 14 Self Test Question What is the IUPAC (substitutive) name for the following molecule? 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

15 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Properties of Alcohols and Alkyl Halides

16 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 16 Alcohols and Alkyl Halides Are Polar red = higher electron density (partial negative charge) blue = lower/ deficient electron density (partial positive charge)

17 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 17 Effect of Structure on Boiling Points CH 3 CH 2 CH 3 (propane) CH 3 CH 2 F (fluoroethane) CH 3 CH 2 OH (ethanol) MW boiling point (ºC) Dipole moment (µ) only London dispersion forces aka: induced- dipole/induced-dipole induced/induced dipole-dipole attractive force dipole/induced-dipole induced/induced dipole-dipole attractive force dipole/induced-dipole hydrogen bonding

18 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 18 Review: induced-dipole//induced-dipole (London Dispersion Forces) more atoms = more electrons = more induced dipoles = more attractive forces = higher boiling point

19 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 19 Dipole/Induced-Dipole permanent dipole in one molecule induces a temporary dipole in a non-polar region of another molecule more C-X bonds = more dipole/dipole- induced attractive forces

20 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 20 Dipole/Dipole 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.

21 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 21 Hydrogen Bonding is a Strong Dipole/Dipole Attractive Force

22 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 22 Boiling Point Trends in same class (i.e. X = F) boiling point increases as MW increases; more atoms = more attractive van der Waals forces = 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

23 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 23 Boiling Point Trends (Cl, Br, I Only) boiling point increases with increasing number of halogens despite CCl 4 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

24 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 24 Polarizability and Teflon more bonds to F (low polarizability) = less/weaker induced- dipole/induced-dipole attractive forces Teflon® = polytetrafluoroethylene (PTFE)

25 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 25 Polarizability polarizability: the ease of distortion of the electron cloud of a molecular entity by an electric field; “flexibility”, “squishiness” of the electron cloud polarizability increases down the periodic table; larger orbitals; more polarizable = better able to momentarily generate induced-dipole = stronger induced- dipole/induced-dipole forces = more attractive forces = higher boiling point bromomethane (b.p. = 3 ºC) fluoromethane (b.p. = -78 ºC)

26 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 26 Self Test Question Rank the following in order of increasing boiling point. a. b. c. d. A. a, b, c, d B. b, c, d, a C. b, d, c, a D. a, c, b, d E. d, b, c, a highest lowest

27 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Chapter: 15 Organic Reactions Preparation of Alkyl Halides

28 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 28 Preparation of Alkyl Halides from Alcohols 1°, 2° & 3° alcohols react irreversible reaction; no equilibrium here more reactive reactants & substrates = faster reaction

29 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 29 Reactivity of Hydrogen Halides Increasing Reactivity of Hydrogen Halides Toward Alcohols HFHIHClHBr<<< least reactive (slowest) most reactive (fastest) stronger acid (lower pKa) = more reactive increased reactivity = faster reaction remember: irreversible reaction; no equilibrium here

30 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 30 Reactivity of Alcohols more substituted alcohol = more reactive increased reactivity = faster reaction remember: irreversible reaction; no equilibrium here

31 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 31 Higher Energy of Reactants = Increased Reactivity higher energy reactants = if transition states are the same, then lower activation energy (Ea) = faster reaction = more reactive

32 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 32 Lower Energy Transition States = Increased Reactivity higher energy transition states = if reactant energies are close, then lower activation energy (Ea) = faster reaction = more reactive We will explore why 3º alcohols provide lower energy transition states on Thursday.

33 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 33 More Examples think about the pattern of the reaction ignore parts of the molecule that don’t react reaction conditions: generally, above/below rxn arrow more reactive hydrogen halide (HBr) is needed for less reactive secondary alcohols

34 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 34 Alternative Conditions A mixture of sodium bromide and sulfuric acid may be used in place of HBr. reagents generally placed above/below reaction arrow inorganic products usually omitted (assumed)

35 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October º & 2º Alcohols Unreactive Toward HCl Alternative Reagent for Preparation of Alkyl Chlorides thionyl chloride SOCl 2 thionyl chloride reacts rapidly with 1º and 2º alcohols byproducts of the reaction are SO 2 (g) and HCl(g) base is needed to neutralize HCl: e.g. K 2 CO 3, pyridine

36 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 36 Alkyl Halides & Purple Pills Esomeprazole Nexium ®

37 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 37 Self Test Question Predict the organic product of the following reaction... a.b.c. d. A. a B. b C. c D. d E. e e.

38 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 38 Self Test Question Which of the following transformations is unlikely to generate the product indicated? A.a. B.b. C.c. D.d. a. b. c. d. x primary alcohols and HCl are insufficiently reactive

39 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 39 Substitution Reaction hydroxyl grouphalide Hydroxyl group is being substituted (replaced with) a halide

40 University of Illinois at Chicago UIC CHEM 494 Special Topics in Chemistry Chapter 15 Mechanisms of Substitution Reactions

41 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 41 Substitution: How Does it Happen? mechanism: a generally accepted series of elementary steps that show the order of bond breaking and bond making elementary step: a bond making and/or bond breaking step that only involves one transition state break bond make bond

42 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 42 Ingold-Hughes Mechanistic Designators Letter # N or E Designates type of process Designates molecularity Nucleophilic or Electrophilic Example Rate = k x [t- BuOH] SN1SN1 Substitution, nucleophilic, 1st order

43 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 43 Nucleophilic Substitution (S N 1) Step One Proton Transfer (Protonation) pK a = -3.9

44 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 44 Step One Potential Energy Diagram transition state: energy maximum along reaction coordinate for one elementary step; usually involves partial bond making and partial bond breaking intermediate: energy minimum along the reaction coordinate; species with a finite lifetime; neither reactant, nor product Hammond Postulate: structure of the transition state “looks” most like its closest energy reactant or intermediate Step One Proton Transfer (Protonation)

45 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 45 Mechanism: Nucleophilic Substitution (S N 1) Step Two Dissociation (Ionization)

46 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 46 Step Two Potential Energy Diagram largest activation energy (Ea) endothermic, slowest carbocation intermediate is much higher in energy than an oxonium ion carbocations do not have a full octet, whereas oxonium ions do structure of transition state most resembles the closest energy neighbor, the carbocation (Hammond Post.) Step Two Dissociation (Ionization)

47 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 47 Mechanism: Nucleophilic Substitution (S N 1) Step Three Carbocation Capture Cation = ElectrophileAnion = Nucleophile

48 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 48 Step Three Potential Energy Diagram fast step because small activation energy; positive and negative atoms bond fast products are much lower in energy since they are neutral; exothermic reaction transition state looks most like its closest neighbor, the carbocation intermediate (very little C-Cl bond formation at transition state) (Hammond Postulate) Step Three Carbocation Capture

49 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 49 Nucleophiles Add to Electrophiles nucleophile: nucleus loving; Lewis base; electron pair donor; forms bonds with a nucleus that can accept electrons; does not necessarily have to be negatively charged; has available, filled orbitals! electrophile: electron loving; Lewis acid; electron pair acceptor; forms bonds by accepting electrons from other atoms; does not necessarily have to be positively charged; has available, empty orbitals! Cation is Electrophile empty 2p z orbital Chloride is Nucleophile filled n orbital (: = lone pair)

50 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 50 Complete Mechanism

51 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 51 Complete Potential Energy Diagram mechanism only valid for 3º & 2º alcohols reaction is only as fast as its slowest step slowest step (largest Ea) = rate determining step (RDS) here, slowest step is carbocation formation here, RDS is unimolecular Protonation carbocation formation carbocation capture rate determining step (RDS)

52 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 52 Naming the Mechanism: Ingold Notation SN1SN1 S: SubstitutionN: Nucleophilic 1: 1st order (unimolecular) the alcohol functional groups is being substituted with a halide the halide doing the substitution is a nucleophile the RDS is carbocation formation; this step is unimolecular (1st order)

53 UIC University of Illinois at Chicago CHEM 494, Spring 2010 Slide Lecture 5: October 8 53 Self Test Question Consider the S N 1 mechanism for the formation of 2- bromobutane. Which structure best represents the highest energy transition state in this mechanism? A.a. B.b. C.c. D.d. a. b. c. d.


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