# Exercises

Exercise

Which orbitals interact in an $SN2$ reaction?

correct

wrong

partly correct

 The highest occupied molecular orbital (HOMO) of the nucleophile with the lowest unoccupied molecular orbital (LUMO) of the substrate. Yes, that is correct! The lowest occupied molecular orbital (LOMO) of the nucleophile with the highest unoccupied molecular orbital (HUMO) of the substrate. No, sorry. The highest occupied molecular orbital (HOMO) of the substrate with the lowest unoccupied molecular orbital (LUMO) of the nucleophile. Sorry, that is wrong. The highest unoccupied molecular orbital (HUMO) of the nucleophile with the lowest occupied molecular orbital (LOMO) of the substrate. Sorry, that is not correct. The lowest unoccupied molecular orbital (LUMO) of the nucleophile with the lowest unoccupied molecular orbital (LUMO) of the substrate. No, sorry.
Exercise

A bonding interaction between the n orbital of the nucleophile and the bonding σ orbital of the substrate is not possible, as ...

correct

wrong

partly correct

 ... the nucleophile's n orbital, as well as the substrate's σ orbital, are unoccupied. Thus, the resulting bonding and antiboning molecular orbitals would be unoccupied, too. No, sorry. ... the nucleophile's n orbital, as well as the substrate's σ orbital, are just partially occupied. Thus, the resulting bonding and antiboning molecular orbitals would be partially occupied, too. Consequently, the bonding and the antibonding interaction would cancel each other out. Sorry, that is wrong. ... the nucleophile's n orbital, as well as the substrate's σ orbital, are occupied. Thus, the resulting bonding and antiboning molecular orbitals would be occupied, too. Consequently, the bonding and the antibonding interaction would cancel each other out. Yes, that is correct!
Exercise

The strength of the HOMO/LUMO interaction in an $SN2$ reaction depends considerably on ...

correct

wrong

partly correct

 ... the speed with which the nucleophile approaches the substrate. No, sorry. ... the pressure with which the nucleophile approaches the substrate. Sorry, that is wrong. ... the reaction temperature. No, sorry. ... the direction from which the nucleophile approaches the substrate. Yes, that is correct! ... how long the nucleophile's approach to the substrate lasts. Sorry, that is not correct.
Exercise

Which borderline cases of the direction from which the nucleophile approaches the substrate in an $SN2$ reaction are conceivable?

correct

wrong

partly correct

 The nucleophile attacks the substrate along the C-L bonding axis from the side opposite to L. This is called back-side attack. The nucleophile attacks the substrate along the C-L bonding axis from the side opposite to L. This is called top-side attack The nucleophile attacks the substrate along the C-L bonding axis from the side on which L is found. This is called front-side attack. The nucleophile approaches the substrate perpendicularly to the C-L bonding axis. This is called side attack. The nucleophile approaches the substrate perpendicularly to the C-L bonding axis. This is called front attack. The nucleophile attacks the substrate along the C-L bonding axis from the side on which L is found. This is called back-side attack.
Exercise

Which orbitals overlap when the nucleophile approaches the substrate exactly along the C-L bonding axis in a back-side attack?

correct

wrong

partly correct

 The occupied nucleophile's z orbital (lone electron pair) with the LUMO of the substrate. No, sorry. The occupied nucleophile's n orbital (lone electron pair) with the LUMO of the substrate. Correct! The occupied nucleophile's n orbital (lone electron pair) with the HOMO of the substrate. Sorry, that is wrong. The occupied nucleophile's p orbital (lone electron pair) with the LUMO of the substrate. No, sorry. The occupied nucleophile's HOMO (lone electron pair) with the LUMO of the substrate. Yes, that is correct!
Exercise

In an $SN2$ reaction, a front-side attack of the nucleophile on the substrate exactly along the C-L bonding axis is particularly unfavourable. Why?

correct

wrong

partly correct

 Due to electrostatic reasons. No, sorry. Due to the magnetic interactions between the nucleophile and the leaving group. Sorry, that is wrong. Due to the steric hindrance between the nucleophile and the leaving group. Correct!
Exercise

Which disadvantages does a side attack of the nucleophile on the substrate have in an $SN2$ reaction?