CHM 25500 Lecture Notes - Lecture 25: Leaving Group, Electrophile, Nucleophile

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29 Jul 2015

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Chm 255 - lecture 25 - reactions of alkyl halides. Primary alkyl halides contain a carbon attached to a halogen, two hydrogens and one r group. Secondary alkyl halides contain a carbon attached to a halogen, one hydrogen and two r groups. Tertiary alkyl halides contain a carbon attached to a halogen and three r groups. Allylic alkyl halides contain a carbon bonded to a halogen and another carbon that has a double bond (the allylic carbon is not the one with the double bond itself) Benzylic alkyl halides contain a carbon attached to a halogen and a benzyl group (the carbon is not part of the benzyl group) Vinyl alkyl halides contain a carbon with a halogen and a double bond to another carbon. Aryl alkyl halides contain a benzyl group for which one carbon is attached to a halogen. Alkyl halides where the halogen is attached to an sp3 carbon undergo nucleophilic substitution reactions.

Related Questions

Questions:

1) In the tests with sodium iodide in acetone and silver nitrate in ethanol, why should 2-bromobutane react faster than 2-chlorobutane?

2) Why is benzyl chloride reactive in both tests, whereas bromobenzene is unreactive?

3) When benzyl chloride is treated with sodium iodide in acetone, it reacts much faster than 1-chlorobutane, even though both compounds are primary alkyl chlorides. Explain this rate difference.

4) 2-Chlorobutane reacts much more slowly than 2-chloro-2-methylpropane in the silver nitrate test. Explain this difference in reactivity.

5) Bromocyclopentane is more reactive than bromocyclohexane when heated with sodium iodide in acetone. Explain this difference in reactivity.

CHEM 211 Biological Chemistry Lab #8-Factors effecting the reactions of alkylhalides A. Experimental objectives Examine the effects of leaving group, alkyl group structure and solvent polarity on the reaction of alkyl halides Examine the effects of solvent polarity on the reaction of a tertiary alkyl halide with sodium hydroxide To examine SN1 and SN2 reaction conditions To learn the most two important factors that effects the reactivities of alkyl halides in nucleophilic substitution reaction B. Introduction The reactivities of alkyl halides in nucleophilic substitution reactions depend on two important factors: reaction conditions and substrate structure. The reactivities of the several substrate types will be examined under both SN1 and SN2 reaction conditions in this experiment A reagent composed of sodium iodide or potassium iodide dissolved in acetone is useful in classifying alkyl halides according to their reactivity in an SN2 reaction. Iodide is an excellent nucleophile, and acetone is a nonpolar solvent. Thetendency to form a precipitate increases the completeness of the reaction. Sodiumiodide and potassium iodide are soluble in acetone, but the corresponding bromidesand chlorides are not soluble. Consequently, as bromide ion or chloride ion is produced, the ion is precipitated from the solution. According to LeChatelier' s Principle, the precipitation of a product from the reaction solution drives the equilibrium toward the right such is the case in the reaction described here R-Cl Na RI NaCl (s) R-Br Na RI-NaBr (s) A reagent composed of silver nitrate dissolved in ethanol is useful in classifying alkyl halides according to their reactivity in an SN1 reaction. Nitrate ion is a poor nucleophile and ethanol is a moderately powerful ionizing solvent. The silver ion, because of its ability to coordinate the leaving halide ion to form a silver halide precipitate ,greatly assists the ionization of the alkyl halide. Again a precipitate as one of the reaction products also enhances the reaction C2H5OH R OC2H5 CI Ag AgCl (s) Page 1 of 5

Classify each of the following statements as true or false:

a) To be classified as organic, a compound must be or have been part of a living organism.

b) Carbon atoms normally form four bonds in organic compounds.

c) Only an unsaturated hydrocarbon can engage in an addition reaction.

d) Members of a homologous series differ by a distinct structural unit.

e) Alkanes, alkenes, and alkynes are unsaturated hydrocarbons.

f) Alkyl groups are a class of organic compounds.

g) Isomers have the same molecular formulas but different structural formulas.

h) Cis-trans isomerism appear among alkenes but not alkynes.

i) All aliphatic hydrocarbons are unsaturated.

j) Aromatic hydrocarbons have a ring structure.

k) An alcohol has an alkyl group bonded to an oxygen atom, and an ether has two.

l) Carbonyl groups are found in alcohols and aldehydes.

m) An ester is an aromatic carbon made from the reaction of an alcohol and a carboxylic acid.

n) An amine has one, two, or three alkyl groups substituted for hydrogens in an ammonia molecule.

o) An amide has the structure of a carboxylic acid except that replaces OH in the carboxyl group.

p) A peptide linkage series arises when a water molecule forms from a hydrogen from the of one amino acid molecule an from an another amino acid molecule.

r) Chain-growth polymers are made a reaction that gives off water a second product.

s) Nylon is an example of a step-growth condensation polymer.

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CHM 25500 Lecture Notes - Lecture 25: Leaving Group, Electrophile, Nucleophile

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