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.
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(-) neomenthol
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(+) neomenthol
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Minty - musty – fresh – earthy campherous – some cooling
Taste threshold = 600 ppb
Cooling threshold = 25000 ppb
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Minty - musty – fresh – some cooling - sweet
Taste threshold = 500 ppb
Cooling threshold = 2500 ppb
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(-) menthol
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(+) menthol
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Very cooling – sweet – fresh - minty
Taste threshold = 400 ppb
Cooling threshold = 800 ppb
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Fresh – cooling – minty with musty – bitter
Taste threshold = 300 ppb
Cooling threshold = 3000 ppb
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(-) isomenthol
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(-) isomenthol
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Musty - sweet– hay – earthy camphoraceous – herbaceous – slight cooling.
Taste threshold = 600 ppb
Cooling threshold = 30000 ppb
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Musty – woody – fresh – carrot minty - earthy camphoraceous –slight cooling.
Taste threshold = 700 ppb
Cooling threshold = 7000 ppb
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(-) neoisomenthol
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(+) neoisomenthol
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Minty – earthy – woody – camphoraceous – sweet – minty – slight cooling
Taste threshold = 1000 ppb
Cooling threshold = 6000 ppb
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Minty – earthy – woody – camphoraceous – carrot – minty – herbaceous - very little cooling
Taste threshold = 200 ppb
Cooling threshold = 25000 ppb
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R or S Menthol?
Answers:
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