Alkyl Halides and C-X Bond Polarity

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Questions and Answers

What is the main product formed when propene reacts with hydrogen bromide?

(CH3)2CHBr

CH3CH2CH2Br

CH3CHBrCH3 (correct)

All of the above

Which of the following is NOT a characteristic of the Finkelstein reaction?

It is used to prepare alkyl iodides.

The reaction is driven by the precipitation of NaCl or NaBr.

It involves the reaction of an alkyl chloride or bromide with NaI in dry acetone.

It is an example of a SN1 reaction. (correct)

What is the primary driving force behind the Finkelstein reaction?

The formation of a precipitate of NaCl or NaBr. (correct)

The high reactivity of NaI in dry acetone.

The liberation of heat during the reaction.

The formation of a more stable carbocation intermediate.

Why is the addition of bromine in CCl4 to an alkene a useful test for the presence of a double bond?

The reaction results in the discharge of the reddish-brown color of bromine. Signup and view all the answers

Which of the following statements is TRUE about the free radical monochlorination of (CH3)2CHCH2CH3?

The reaction produces a mixture of monochloro isomers. Signup and view all the answers

What is the name of the product formed when bromine is added to an alkene?

Vic-dibromide Signup and view all the answers

Which of the following conditions would favor the formation of the more stable carbocation intermediate in the addition of hydrogen bromide to an alkene?

The presence of a tertiary carbon atom. Signup and view all the answers

Which of the following is the most likely product of the reaction between 2-methylpropene and hydrogen bromide?

2-bromo-2-methylpropane Signup and view all the answers

In the synthesis of vic-dibromides, what is the primary role of the halogenating reagent?

To form a carbocation intermediate, facilitating the attack of a bromine anion from both sides. Signup and view all the answers

What is the key principle that dictates the major product in an elimination reaction of a haloalkane, as described by Zaitsev's rule?

The thermodynamic stability of the alkene products, with the more substituted alkene being favored. Signup and view all the answers

How does Le Chatelier's principle apply to the Finkelstein reaction, where a primary alkyl halide is converted to an alkyl iodide using sodium iodide in acetone?

The addition of sodium iodide shifts the equilibrium towards the formation of the alkyl iodide due to the formation of a less soluble salt, sodium bromide. Signup and view all the answers

In the halogenation of alkanes, what factor primarily determines the regioselectivity of the reaction, i.e., which carbon atom is most likely to be halogenated?

The relative stability of the resulting alkyl radical intermediates. Signup and view all the answers

Why is the attack of a nucleophile on a carbocation possible from either side of the plane?

Due to the planar geometry of the carbocation, the nucleophile can approach from both sides with equal probability. Signup and view all the answers

Which statement best describes the formation of an alkene in an elimination reaction involving a haloalkane?

The removal of a hydrogen atom and a halogen atom from adjacent carbon atoms leads to the formation of a double bond between those carbons. Signup and view all the answers

What is the major product formed when 2-bromopentane undergoes dehydrohalogenation with alcoholic potassium hydroxide?

Pent-2-ene Signup and view all the answers

Which of the following factors can influence the rate of an elimination reaction of a haloalkane?

All of the above factors can influence the rate of an elimination reaction. Signup and view all the answers

Which method effectively leads to the formation of pure alkyl halides?

Using thionyl chloride Signup and view all the answers

As you move down the group of halogens, what is the trend observed in carbon-halogen bond lengths?

Bond lengths increase from C–F to C–I Signup and view all the answers

What happens to the dipole moment as the size of the halogen atom increases?

It can either increase or decrease depending on the halogen Signup and view all the answers

Which carbon-halogen bond has the highest bond enthalpy?

C–F Signup and view all the answers

Which of the following reactions primarily leads to vic-dibromides?

Addition of bromine across a double bond Signup and view all the answers

How does Le Chatelier's Principle apply to the synthesis of haloalkanes?

Adding more reactants shifts the equilibrium to the right Signup and view all the answers

Which reaction is known for substituting iodine in haloalkanes with another halogen?

Finkelstein reaction Signup and view all the answers

What is a common misconception about the carbon-halogen bond's polarity?

All carbon-halogen bonds are non-polar Signup and view all the answers

Study Notes

Addition Reactions of Alkenes

Alkenes undergo addition reactions with hydrogen halides (HCl, HBr, HI) to convert into corresponding alkyl halides.
Propene example shows that two products are formed, but one predominates due to Markovnikov’s rule.

Bromine Addition for Detection

Addition of bromine in carbon tetrachloride (CCl4) is used to detect double bonds; the reddish-brown color of bromine disappears.
The process results in the formation of vic-dibromides, which are colorless.

Monochlorination Isomers

Free radical monochlorination of (CH3)2CHCH2CH3 yields several monochloro structural isomers:
- (CH3)2CHCH2CH2Cl
- (CH3)2CHCH(Cl)CH3
- (CH3)2C(Cl)CH2CH3
- CH3CH(CH2Cl)CH2CH3

Finkelstein Reaction

Alkyl iodides can be synthesized by reacting alkyl chlorides or bromides with NaI in dry acetone.
NaCl or NaBr precipitate, driving the reaction forward per Le Chatelier’s Principle.

Carbon-Halogen Bond Characteristics

Halogen atoms are more electronegative than carbon, leading to polarized C-X bonds: carbon bears a partial positive charge, halogen bears a partial negative charge.
Bond length increases from C-F to C-I due to the increasing size of halogen atoms.

Carbon-Halogen Bond Data

Typical data for bond lengths, bond enthalpies, and dipole moments include:
- CH3–F: 139 pm, 452 kJ/mol, 1.847 Debye
- CH3–Cl: 178 pm, 351 kJ/mol, 1.860 Debye
- CH3–Br: 193 pm, 293 kJ/mol, 1.830 Debye
- CH3–I: 214 pm, 234 kJ/mol, 1.636 Debye

Preparation of Haloalkanes

Haloalkanes can be made by replacing the hydroxyl group of an alcohol using concentrated halogen acids, phosphorus halides, or thionyl chloride.
Thionyl chloride is preferred because it generates gaseous products (SO2 and HCl) that escape, leading to pure alkyl halides.

Elimination Reactions

Heating haloalkanes with b-hydrogen atoms in alcoholic potassium hydroxide leads to elimination reactions, resulting in alkene formation.
The elimination produces the major product according to Zaitsev’s rule, which states that the more substituted alkene is favored.
Example: 2-bromopentane yields pent-2-ene as the major product due to greater alkyl group attachments on the double bond.

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Description

Learn about the polarity of carbon-halogen bonds in alkyl halides, and how the size of halogen atoms affects the bond. Understand the partial charges on carbon and halogen atoms.