Which of the following molecules is chiral? How is this determined?
3,4-dimethyl-1-pentene
2-bromobutanamide
2-bromo-1-butanol
chlorocyclohexane
cis-1,2-dimethylcyclobutane
trans-1,2-dimethylcyclobutane
1-pentanenitrile
3-pentanamine
2-aminopropanoic acid (common name: alanine)
2,3-dibromobutane
3,4-dimethyl-1-pentene
2-bromobutanamide
2-bromo-1-butanol
chlorocyclohexane
cis-1,2-dimethylcyclobutane
trans-1,2-dimethylcyclobutane
1-pentanenitrile
3-pentanamine
2-aminopropanoic acid (common name: alanine)
2,3-dibromobutane
1 Answer
WARNING! Long answer. You look for chiral carbons and internal planes of symmetry.
Explanation:
A chiral carbon is a carbon with four different groups attached.
An internal plane of symmetry is a plane that divides the molecule that are mirror images of each other.
3,4-dimethylpent-1-ene
Two chiral carbons, no plane of symmetry. ∴ Chiral.
2-Bromobutanamide
One chiral carbon, no plane of symmetry. ∴ Chiral.
2-Bromobutan-1-ol
One chiral carbon, no plane of symmetry. ∴ Chiral.
Chlorocyclohexane
No chiral carbon. ∴ Not chiral.
cis-1,2-Dimethylcyclobutane
Two chiral carbons, but an internal plane of symmetry. ∴ Not chiral.
trans-1,2-Dimethylcyclobutane
Two chiral carbons, no internal plane of symmetry. ∴ Chiral.
Pentanenitrile
No chiral carbons. ∴ Not chiral.
Pentan-3-amine
No chiral carbons. ∴ Not chiral.
2-Aminopropanoic acid
One chiral carbon, no internal plane of symmetry. ∴ Chiral.
2,3-Dibromobutane
This has both chiral and achiral forms.
Two chiral carbons, but an internal plane of symmetry. ∴ Not chiral.
Two chiral carbons, no internal plane of symmetry. ∴ Chiral.
