05 Alkanes and Radical Reactions Free Online FlashCards

What is the general formula for an acyclic alkane?

Acyclic alkanes have the general formula $C_nH_{2n+2}$.

What is an alkane conformation?

Conformations are different spatial arrangements produced by rotation around single bonds; they usually interconvert rapidly.

What happens in radical halogenation of an alkane?

Radical halogenation replaces an alkane hydrogen with a halogen, usually chlorine or bromine, under light or heat.

What is bond dissociation energy, and how can bond energies estimate $\Delta H$?

Bond dissociation energy is the energy required to break a bond homolytically into two radicals in the gas phase. Estimate reaction enthalpy with $\Delta H \approx \sum D(\text{bonds broken})-\sum D(\text{bonds formed})$.

What geometry and bond angle are typical around an alkane carbon?

Each alkane carbon is approximately tetrahedral, with bond angles near $109.5^\circ$.

What does a Newman projection show?

A Newman projection depicts a molecule viewed directly along a selected carbon–carbon bond; the front carbon is a dot and the rear carbon is a circle.

Which ethane conformation is lower in energy, and what is the energy difference called?

Staggered ethane is lower in energy than eclipsed ethane. Their energy difference is called torsional strain.

How do the anti and gauche conformations of butane differ?

In butane, anti places the methyl groups $180^\circ$ apart and is lower in energy than gauche, where they are $60^\circ$ apart.

What occurs during initiation in radical halogenation?

Initiation uses light or heat to break the halogen bond homolytically, producing two halogen radicals: $\mathrm{X_2 \rightarrow 2X\cdot}$.

What products form when a halogen radical abstracts hydrogen from an alkane?

A halogen radical abstracts hydrogen from an alkane, forming hydrogen halide and an alkyl radical: $\mathrm{X\cdot + R-H \rightarrow H-X + R\cdot}$.

How does the second propagation step continue the radical chain?

The alkyl radical reacts with another halogen molecule to form an alkyl halide and regenerate a halogen radical: $\mathrm{R\cdot + X_2 \rightarrow R-X + X\cdot}$.

What defines a termination step in radical halogenation?

Termination occurs when two radicals combine, removing radicals from the chain; for example, $\mathrm{R\cdot + X\cdot \rightarrow R-X}$.