This is presumably due to the need for a higher intake to achieve a comparable desired effect, not that the gene led to a disposition for greater incentive of habituation. Chemistry
Pure anhydrous caffeine is a bitter-tasting, white, odorless powder with a melting point of 235–238 °C. Caffeine is moderately soluble in water at room temperature (2 g/100 mL), but very soluble in boiling water (66 g/100 mL). It is also moderately soluble in ethanol (1.5 g/100 mL). It is weakly basic (pKa of conjugate acid = ~0.6) requiring strong acid to protonate it. Caffeine does not contain any stereogenic centers and hence is classified as an achiral molecule.The xanthine core of caffeine contains two fused rings, a pyrimidinedione and imidazole. The pyrimidinedione in turn contains two amide functional groups that exist predominantly in a zwitterionic resonance the location from which the nitrogen atoms are double bonded to their adjacent amide carbons atoms. Hence all six of the atoms within the pyrimidinedione ring system are sp2 hybridized and planar. Therefore, the fused 5,6 ring core of caffeine contains a total of ten pi electrons and hence according to Hückels rule is aromatic. Synthesis
The biosynthesis of caffeine is an example of convergent evolution among different species.Caffeine may be synthesized in the lab starting with dimethylurea and malonic acid.Commercial supplies of caffeine are not usually manufactured synthetically because the chemical is readily available as a byproduct of decaffeination. Decaffeination
Extraction of caffeine from coffee, to produce caffeine and decaffeinated coffee, can be performed using a number of solvents.
A webbed neck, or pterygium colli, is a congenital skin fold that runs along the sides of the neck down to the shoulders. There are many variants. Signs and symptoms
On babies, webbed neck may look like loose folds of skin on the neck. As the child grows, the skin may stretch out to look like there is little or no neck. Associated conditions
It is a feature of Turner syndrome (only found in girls) and Noonan syndrome, as well as the rarer Klippel–Feil syndrome, or Diamond–Blackfan anemia

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