Y12 HW Quiz: Radical substitution, Pi, sigma bonds

What are the 3 steps of radical substitution of alkanes?

• Boiling, Melting, Freezing

• Evaporation, Condensation, Sublimation

• Oxidation, Reduction, Precipitation

• Initiation, Propagation, Termination

What will the final charge of the highlighted (yellow) carbon atom be?

(The middle arrow points to the C-C bond, not the carbon atom itself)

• +1

• 0 / Neutral

• -1

• +0.5

Two fish-hook / half-head arrows coming together shows:

• The movement of two single electrons together to form a bond

• The homolytic fission of a bond

• The movement of two pairs of electrons to form a bond

• The heterolytic fission of a bond

Explain the process of initiation in radical substitution of alkanes.

• The breaking of a covalent bond to form two ions.

• The breaking of a covalent bond to form two radicals.

• The formation of a double bond between two carbon atoms.

• The addition of a hydrogen atom to an alkane molecule.

What is termination in radical substitution of alkanes?

• Conversion of a radical into an alkane

• Formation of a highly reactive molecule

• Breaking of a stable molecule into two radicals

• Combination of two radicals to form a stable molecule

What is the role of termination in radical substitution of alkanes?

• Termination only occurs in the presence of alkenes

• Termination has no effect on the substitution of alkanes

• Termination helps in stopping the chain reaction and prevents excessive substitution of alkanes.

• Termination increases the rate of substitution of alkanes

Electrophiles are best described as...

• Species that are attracted to and form bonds by accepting electron density.

• Species that are repelled from electrons, using their own electron density.

• Species that use their lone pairs to attack other species.

• Species that are either positive or neutral, hence can make bonds with negative species.

Which statement best explains whether AlCl₃ is an electrophile or nucleophile?

• The chlorine atoms have lone pairs. Therefore aluminium trichloride is a nucleophile.

• Aluminium is less electronegative than Cl, so has a δ+ charge which makes it susceptible to being attacked by a pair of electrons.

  Therefore AlCl₃ is electrophilic.

• The bond is polarised such that the electropositive Al withdraws electron density from the surrounding Cl atoms. The chlorine atoms are made electropositive and therefore susceptible to being attacked by a pair of electrons.

  Therefore AlCl₃ is an electrophile.

• AlCl₃ is neutral, and not negative. Negative species often act as nucleophiles, so AlCl₃ is an electrophile.

How does sigma bonding differ from pi bonding?

• Sigma bonding is only found in molecules with double bonds, while pi bonding is only found in molecules with single bonds.

• Sigma bonding involves the overlap of p orbitals, while pi bonding involves the overlap of s orbitals.

• Sigma bonding is weaker than pi bonding.

• Sigma bonding involves head-on overlap of atomic orbitals, while pi bonding involves sideways overlap of atomic orbitals.

Sigma vs. pi bonding, which is stronger and why?

• Sigma bonding, because sigma involves head-on overlap, vs the side-on overlap in pi

• Pi bonding because it always is additional to sigma bonding

• Pi bonding, because pi involves side-on overlap, vs the head-on overlap in sigma

• Sigma bonding, because you cannot have pi bonding without sigma bonding first.