Hydrocarbon Reactions Worksheet - Hydrocarbon Reactions Worksheet ... - Free Printable

Problem: Hydrocarbon Reactions Worksheet

#### Section 1: Give the structure of the major organic product of the following reactions.

1. a. Hexane and chlorine
- Reaction: Free radical chlorination of hexane.
- Explanation: Chlorine reacts with hexane in the presence of light (UV radiation) to form a mixture of monochloro, dichloro, etc., derivatives. The most likely product is a monochlorinated derivative due to the high reactivity of primary hydrogens.
- Major Product: 1-Chlorohexane or 2-Chlorohexane (both are possible, but 1-chlorohexane is slightly more favored due to primary hydrogen reactivity).
- Structure:
```
CH3-CH2-CH2-CH2-CH2-CH2Cl
```

2. b. 1-Hexene and chlorine
- Reaction: Addition of chlorine to an alkene (electrophilic addition).
- Explanation: Chlorine adds across the double bond in 1-hexene, forming a vicinal dichloride.
- Major Product: 1,2-Dichlorohexane.
- Structure:
```
CH3-CH(Cl)-CH2-CH2-CH2-CH3
```

3. c. 1-Hexene and hydrogen chloride gas
- Reaction: Electrophilic addition of HCl to an alkene.
- Explanation: HCl adds across the double bond, with the hydrogen atom attaching to the less substituted carbon (Markovnikov's rule).
- Major Product: 2-Chlorohexane.
- Structure:
```
CH3-CH2-CH(Cl)-CH2-CH2-CH3
```

4. d. 1-Hexyne and excess chlorine
- Reaction: Addition of chlorine to an alkyne.
- Explanation: Excess chlorine will add across both the triple bond carbons, forming a vicinal dichloride.
- Major Product: 1,2-Dichlorohexane.
- Structure:
```
CH3-CH(Cl)-CH2-CH2-CH2-CH3
```

5. e. 1-Hexene and dilute sulfuric acid
- Reaction: Acid-catalyzed hydration of an alkene.
- Explanation: Dilute sulfuric acid adds water across the double bond, forming an alcohol. The product follows Markovnikov's rule.
- Major Product: 2-Hexanol.
- Structure:
```
CH3-CH2-CH(OH)-CH2-CH2-CH3
```

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#### Section 2: Comment on the following observations.

1. a. Hydrocarbons have low boiling points compared to other organic compounds of similar formula weights.
- Comment: Hydrocarbons have only weak London dispersion forces (van der Waals forces) as intermolecular interactions because they lack polar functional groups. Other organic compounds, such as alcohols or acids, have stronger intermolecular forces like hydrogen bonding or dipole-dipole interactions, which raise their boiling points. Therefore, hydrocarbons generally have lower boiling points.

2. b. There are no cyclic alkynes, nor are there any cis/trans isomers of alkynes.
- Comment:
- Cyclic Alkynes: Cyclic alkynes are highly strained due to the linear geometry of the triple bond (180° bond angles). This strain makes them unstable and energetically unfavorable, so they do not exist in significant quantities.
- Cis/Trans Isomers of Alkynes: Alkynes have a linear geometry around the triple bond, meaning all atoms attached to the triple bond are collinear. This arrangement does not allow for cis/trans isomerism because there is no possibility of different spatial arrangements of substituents around the triple bond.

3. c. Treatment of an alkane with chlorine requires UV radiation to cause reaction, whereas an alkene will react instantly.
- Comment:
- Alkanes: Alkanes undergo free radical substitution reactions with chlorine, which require UV radiation to initiate the homolytic cleavage of the Cl-Cl bond, forming chlorine radicals. These radicals then abstract hydrogens from the alkane, leading to substitution.
- Alkenes: Alkenes undergo electrophilic addition reactions with chlorine, where the π electrons of the double bond directly attack the electrophilic chlorine molecule. This process does not require UV radiation and occurs much faster than the free radical mechanism of alkanes.

4. d. The product of the reaction of an alkane with chlorine is unpredictable.
- Comment: When an alkane reacts with chlorine (free radical chlorination), the reaction proceeds via a chain mechanism involving multiple steps. The products depend on the relative reactivity of different types of hydrogens (primary, secondary, tertiary) and the conditions of the reaction. Since the reaction can produce a variety of mono-, di-, tri-, etc., chlorinated products, the exact composition of the product mixture is difficult to predict without detailed kinetic data.

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Final Answer:

\boxed{
\text{See detailed explanations above.}
}