01:160:307 Chapter Notes - Chapter 10: Methyl Radical, Pi Bond, Bayerischer Rundfunk

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limeantelope48

3 May 2016

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Rutgers University

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Chemistry

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01:160:307

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No reaction when an aromatic molecule is mixed with br2. During a demonstration by dr. h, the reactants changed colors when held against light. This is a substitution reaction, but what kind: sn2 no! There"s no leaving group: sn1 no! This symbol is a fishhook, which has half of an arrow head. This means that only one electron is moving (instead of a pair of electrons) h (or heat) The br br bond weakens with heat or light (it takes 46 kcal/mol to break it). Each electron in the bond goes to a different br. Tthhrreeee ffaatteess ooff rraaddiiccaallss:: addition to pi bond. The bromine radical and one electron from a pi bond form a new bond on the least substituted end of the alkene. The other electron in the pi bond is transferred to the more stable carbon atom (making a.

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Nucleophilic Substitution â Synthesis of an Alkyl Halide

Introduction

Alkyl halides can be prepared from alcohols by reactions with hydrogen halides (HCl, HBr, or HI) via nucleophilic substitution. In this type of reaction, the nucleophile displaces a leaving group from a carbon atom of an organic substrate (here the alcohol once protonated). Both electrons of the new bond to the carbon are provided by the nucleophile while the leaving group departs with both electrons of its bond to the substrate. There are two limiting mechanisms that are most common in describing nucleophilic substitution reactions at sp3 carbon centres : (1) a direct displacement (SN2) process and (2) a process that generates an intermediate carbocation (SN1). Which mechanism is a better description depends on the structure of the molecule containing the leaving group, the nature of the leaving group, the size of the nucleophile, and the polarity of the solvent. This experiment is a near-perfect example of an SN1 substitution. H3C OH CH3 H3C + HCl H3C Cl CH3 H3C + H2O (Equation 1) In this reaction, you will prepare 2-chloro-2-methylpropane (t-butyl chloride) from 2- methyl-2-propanol (t-butyl alcohol) using HCl as the strong acid and chloride source. Note that HCl first activates the alcohol in an acid/base reaction before the SN1 reaction proceeds. The final product is characterized by its yield, boiling point, and density. The presence of a halide atom is confirmed with a silver nitrate test.

1) State which of the electrophiles given below will react preferentially by i) SN1, ii) by SN2, or iii) capable of reacting by either of the two mechanisms depending on the given conditions. How can you affect those conditions to favour SN1 or SN2? Reason your predictions based on the structures of the compounds. Br-CH3, Br-CH2CH3, Br-CH(CH3)2, Br-C(CH3)3, Br-CH2-C5H6; C5H6 = phenyl

2) Rank the nucleophiles given below based on high, mediocre, and low nucleophilicity and reason why based on their structures. HO-CH3, H2N-CH3, KO-CH3, KO-C(CH3)3

3) Name two solvents that are commonly used for SN2 reactions. because they considerably slow down SN1 reactions.

4) Can you ever have only SN2 or only SN1?

5) Iodine is a better leaving group than bromine. But iodine is a better nucleophile than bromine. Why is that?

6) Using orbitals, draw the transition state of the SN2 reaction between sodium cyanide and bromomethane. Which orbitals are interacting with which? Why is the bond breaking? Why is the orientation important? Is there another angle besides backside attack that could theoretically work based on orbital geometry? Why doesnât this happen?

7) Name four reagents you can use to dry solvent. Why do we use magnesium sulfate in this lab instead of them?

8) Draw a mechanism with all the proper arrows for the reaction from this experiment.

9) What are we removing with the water wash? Why donât we just add the sodium bicarbonate directly to the reaction mixture instead of doing a water wash?

1. Which of the following reagent(s) can be used to prepare a mixture of o and p-nitro toluene from toluene

(A) HNO₂ (B) HNO₃ (C) HNO₃/Fe (D) HNO₃/H₂SO₄ (E) NaNO₂

(A) H₂SO₃ (B) SO₃/ Which of the following reagent(s) can be used to convert nitrobenzene to m-nitrobenzenesulfonic acid Fe (C) H₂SO₃/Fe (D) H₂SO₄/Al₂(SO₄)₃ (E) H₂SO₄.SO₃

3. Which of the following reagent(s) can be used to prepare bromobenzene from benzene

(A) NBS (B) Br₂/FeBr₃ (C) H₂SO₄/Br₂ (D) Br₂/AlBr₃ (E) Br₂/Pd

4. Which of the following functional groups are o,p-directing ?

(A) Br, CH₂CH₃, NH₂ (B) Cl, NH₂, COOH (C) I, SO₃H, OH (D) OCH₃, Cl, COCH₃ (E) NO₂, CH₃, OH

5. Which of the following reagent(s) gives the reaction below

(A) CH₃Cl (B) Cl₂/ Fe (C) Cl₂/ AlCl₃ (D) Cl₂/ FeCl₃ (E) Cl₂/ HCl

6. Friedal-Craft acylation reagent(s)

(A) CH₃Cl/AlCl₃ (B) Cl₂/CH₃COCl (C) CH₃COCl/AlCl₃ (D) CH₃COCl/FeCl₃ (E) CH₃Cl/FeCl₃

7. Which of the following functional groups are m-directing ?

(A) NO₂, CH₃, OH (B) Br, NH₂, COOH (C) I, SO₃H, OH (D) OCH₃, Cl, COCH₃ (E) COCH_3, SO₃H, CHO

8. Which of the following compound can be used in the Diels-Alder reaction

(A) 2-methyl, 2,4-hexadiene (B) 2,5-hexadiene (C) 1-methyl,cyclohexa-1,4-diene (D) cyclohexa-1,4-diene

(E) 2-methyl, 1,5-hexadiene

9. Which statement about benzene is incorrect?

(A) The Cï¿½C p - bonding is delocalized (B) The C₆ ring is planar (C) The average C - C bond distance is the same as C-C double bonds (D) Each C atom is sp² hybridized ( E ) There are 12 s (sigma) bonds in benzene

10. Which of the following is NOT aromatic

(A) Cyclopropenyl cation (C₃H₃⁺) (B) Benzene (C₆H₆) (C) [16]-Annulene (C₁₆H₁₆)

(D) Cycloheptatrienyl cation (C₇H₇⁺) (E) [18]-Annulene (C₁₈H₁₈)

11. Conjugate addition of one equivalent of deuterium bromide (DBr) to 1,3-butadiene gives

(A) 3-bromo, 4-deutero, 1-butene (B) 3-bromo, 4-deutero, 2-butene (C) 4-bromo, 3-deutero, 1-butene (D) 1-bromo, 4-deutero, 2-butene (E) 1-bromo, 4-deutero, 1-butene

12. Which of the following is a conjugated diene

(A) cyclopentadiene (B) 2-methylcyclohexanone (C) 1-methyl,cyclohexa-1,4-diene (D) cyclohexa-1,4-diene

(E) cycloocta-1,5-diene

13. The aromatic compound is

14. Which of the following reaction involves a benzyne mechanism ?

(A) Ph-CH₃ ? Ph-COOH (B) Ph-CH₃ ? Ph-CHO (C) Ph-OH ? Ph-Cl (D) Ph-Cl ? Ph-OH

(E) none of these

15. Which of the following reagent(s) can be used to prepare a mixture of o and p-nitro toluene from

toluene

(A) HNO₂ (B) HNO₃ (C) HNO₃/Fe (D) HNO₃/H₂SO₄ (E) NaNO₂

16. Friedal-Craft alkyation reagent(s)

(A) C₂H₅Cl/AlCl₃ (B) Cl₂/CH₃COCl (C) CH₃COCl/AlCl₃ (D) CH₃COCl/FeCl₃ (E) CH₃Cl/FeCl₃

17. Which of the following functional groups are o,p-directing ?

(A) NO₂, SO₃H, CHO (B) Br, NH₂, COOH (C) I, OH, CH₃ (D) OCH₃, Cl, COCH₃ (E) COCH_3, SO₃H, Br

18. Major product in the reaction of benzene with 1-bromopropane, in the presence of AlBr₃ catalyst

(A) bromobenzene (B) n-propylbenzene (C) iso-propylbenzene (D) o-bromo-n-propylbenzene

(E) p-bromo-n-propylbenzene

19. Which of the following is the electrophile in the nitration reaction

(A) ⁺HNO₂ (B) NO₂⁺ (C) N₂+ (D) HNO₃/H₂SO₄ (E) NO₃⁺

20. Which of the following is the electrophile in the sulfonation reaction

(A) ⁺HSO₂ (B) SO₂⁺ (C) SO₃⁺ (D) SO₃/H₂SO₄ (E) HSO₃⁺

21. Which of the following is the electrophile in the Friedel-Craft acylation reaction

(A) RCO₂⁺ (B) RCO⁺ (C) CO₂⁺ (D) RX/H₂SO₄ (E) RCO₃⁺

22. The benzyne intermediate has ï¿½ï¿½ p bonds

(A) 1 (B) 2 (C) 3 (D) 4 (E) 5

23. The reagent used for Allylic/benzylic bromination is:

(A) NBS (B) Br₂/ Fe (C) Br₂/ AlBr₃ (D) Br₂/ FeBr₃ (E) Br₂/ HBr

24. Which of the following is an oxidation reagent

(A) H₂SO₄ (B) KMnO₄ (C) KMnO₂ (D) NaBH₄ (E) AlCl₃

25. The formula of fuming sulfuric acid

(A) H₂SO_4.SO₃ (B) H₂SO_4.SO₂ (C) H₂SO_4.HSO₂ (D) H₂SO_4.HSO₃ (E) H₂SO_4.SO

26. How do you prepare the following compounds, starting from benzene ?

(a). aniline (b). Iodo benzene (c). benzoic acid (d). benzylbromide (e). m-methyl benzoic acid

(f). p-nitrobenzoic acid (g) m-nitrobenzoic acid (h). p-chlorobenzenesulfonic acid (i). m-chlorobenzenesulfonic

acid (j) 3-isopropyl benzoic acid (k). 4-isopropyl toluene

27. Draw the product(s) from the following reactions showing the mechanisms

(a) 1,3-butadiene with acrylonitrile

(b) 1,3-butadiene with one eqv. HBr

(d) 1,3-cyclohexadiene with one eqv. HBr

(e) 1,3-cyclohexadiene with two eqv. HBr

(f) cyclopentadiene with two eqv. HBr

28. How do you prepare the following compounds, starting from toluene ?

(a). benzoic acid (b). benzyl alcohol (c). m-bromobenzoic acid (d). m-methylbenzoic acid (e). m-nitro

benzoic acid (f). p-nitrobenzoic acid

29. What is/are the product(s) expected when ethylbenzene is reacted with

(a). NBS

(b). Br₂/FeBr₃

(c). KMnO₄, then H⁺

(d). fuming H₂SO₄

(e). NBS, then aq. NaOH

(f) iso-butylbromide/AlBr₃

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01:160:307 Chapter Notes - Chapter 10: Methyl Radical, Pi Bond, Bayerischer Rundfunk

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