Steriochemistry of menthol:
Objective: Determine the configuration of Chiral C atoms in each stereoisomer of menthol.
- Menthol has 8 stereoisomers. They also have different characteristics.
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Note: that the missed bond are bonds with H.
- (L) - menthol and (D) – menthol are mirror images and not superimposable , thus they are enantiomers and that's why they have same melting points ( since enantiomers have same physical properties).
Characteristics of each stereoisomer of menthol. |
|
(-) neomenthol |
(+) neomenthol |
Minty - musty – fresh – earthy campherous – some cooling Taste threshold = 600 ppb Cooling threshold = 25000 ppb |
Minty - musty – fresh – some cooling - sweet Taste threshold = 500 ppb Cooling threshold = 2500 ppb |
(-) menthol |
(+) menthol |
Very cooling – sweet – fresh - minty Taste threshold = 400 ppb Cooling threshold = 800 ppb |
Fresh – cooling – minty with musty – bitter Taste threshold = 300 ppb Cooling threshold = 3000 ppb |
(-) isomenthol |
(-) isomenthol |
Musty - sweet– hay – earthy camphoraceous – herbaceous – slight cooling. Taste threshold = 600 ppb Cooling threshold = 30000 ppb |
Musty – woody – fresh – carrot minty - earthy camphoraceous –slight cooling. Taste threshold = 700 ppb Cooling threshold = 7000 ppb |
(-) neoisomenthol |
(+) neoisomenthol |
Minty – earthy – woody – camphoraceous – sweet – minty – slight cooling Taste threshold = 1000 ppb Cooling threshold = 6000 ppb |
Minty – earthy – woody – camphoraceous – carrot – minty – herbaceous - very little cooling Taste threshold = 200 ppb Cooling threshold = 25000 ppb |
R or S Menthol?