Hydrocarbons Lecture Review

This set of flashcards covers key concepts from the hydrocarbons lecture, focusing on alkanes, alkenes, alkynes, and various reactions involving them.

What are the general formulas for alkanes, alkenes, and alkynes?

Alkanes: CnH2n+2; Alkenes: CnH2n; Alkynes: CnH2n-2.

What is the process called when hydrogen is added to alkenes and alkynes?

Hydrogenation.

What is the key characteristic of the hydrogenation mechanism of alkenes?

It involves a four-membered cyclic transition state and is an exothermic process.

What are the typical catalysts used in the hydrogenation of alkenes and alkynes?

Platinum (Pt), Nickel (Ni), and Palladium (Pd).

What happens to the rate of reaction of alkynes compared to alkenes during hydrogenation?

The rate of reaction of alkynes is typically greater than that of alkenes due to their structure.

What is syn addition in the context of hydrogenation?

Both hydrogen atoms are added to the same side of the double or triple bond.

Define stereochemistry in the context of cis- and trans-alkenes.

Stereochemistry refers to the spatial arrangement of atoms in molecules; cis-alkenes have substituents on the same side, while trans-alkenes have them on opposite sides.

What is the significance of a four-membered cyclic transition state in hydrogenation?

It allows for the simultaneous bonding of hydrogen to both carbons of a double or triple bond.

What is the primary difference in reactivity between 1°, 2°, and 3° halides in reactions such as the Wurtz reaction?

1° R-X > 2° R-X > 3° R-X in terms of reactivity.

In the context of free radical halogenation, what is the order of reactivity among halogens?

F2 > Cl2 > Br2 > I2.

What type of reaction occurs during the addition of hydrogen halides to alkenes?

Electrophilic addition.

What is Markovnikov's rule in the context of addition reactions?

The more electronegative part of the reagent adds to the carbon atom with the greater number of hydrogens.

What stabilizes a free radical during a reaction?

Stability is increased with more substituted radicals, with tertiary radicals being the most stable.

How does the presence of inhibitors affect free radical reactions?

Inhibitors reduce the rate of free radical reactions by terminating chain reactions.

What product is formed from ozonolysis of alkenes?

Ozonolysis can form carbonyl compounds such as aldehydes or ketones.

Explain the significance of regioselectivity in reactions involving alkenes.

Regioselectivity refers to the preference of one direction of chemical bond making or breaking over all other possible directions.

What is the product of the Wurtz reaction involving dihalides?

The Wurtz reaction produces alkanes by coupling alkyl halides.

What are alkanes?

Alkanes are saturated hydrocarbons with only single bonds between carbon atoms, following the general formula CnH(2n+2).

What are alkenes?

Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond, following the general formula CnH(2n).

What is the main difference between alkanes and alkenes?

The main difference is that alkanes contain only single bonds, while alkenes contain at least one double bond.

Give an example of a simple alkane.

An example of a simple alkane is methane (CH₄).

Give an example of a simple alkene.

An example of a simple alkene is ethene (C₂H₄).

What is the significance of the double bond in alkenes?

The double bond in alkenes allows for the possibility of additional chemical reactions compared to alkanes.

How can you identify alkenes in a chemical reaction?

Alkenes can be identified through their reaction with bromine water, which leads to decolorization.

What is the boiling point trend for alkanes and alkenes?

Both alkanes and alkenes have increasing boiling points with increasing molecular weight, but alkenes tend to have slightly lower boiling points than alkanes of similar molecular weight.

What is the IUPAC name of the alkane with the formula C₅H₁₂?

The IUPAC name of the alkane with the formula C₅H₁₂ is pentane.

What is the reaction type involved when alkenes undergo hydrogenation?

The reaction type involved when alkenes undergo hydrogenation is an addition reaction.

Which alkane has the highest boiling point: C₈H₁₈, C₇H₁₆, or C₆H₁₄?

C₈H₁₈ (octane) has the highest boiling point among the given alkanes.

What product is formed when ethene reacts with bromine?

When ethene reacts with bromine, 1,2-dibromoethane is formed.

How many isomers can exist for butane (C₄H₁₀)?

There are two structural isomers for butane: n-butane and isobutane.

Explain why alkenes are more reactive than alkanes.

Alkenes are more reactive than alkanes due to the presence of the double bond, which is more reactive than the single bonds in alkanes.

What is the effect of branching on the boiling point of alkanes?

In alkanes, increased branching generally leads to lower boiling points due to decreased surface area and weaker van der Waals forces.

How does the presence of a double bond affect the density of alkenes compared to alkanes?

Alkenes generally have slightly lower densities than alkanes of similar molecular weight due to structural differences.