1) Why is triethylene glycol used instead of ethanol or t-butanol for the solven
ID: 1055497 • Letter: 1
Question
1) Why is triethylene glycol used instead of ethanol or t-butanol for the solvent in E-2 reaction from racemic 1,2-dibromo1,2-diphenylethane?
2) Why is sodium alkoxide (NaOR, such as NaOEt, NaOMe) are stronger bases than NaOH, sodium amide (NaNH2) is stronger base than both hydroxide and alkoxides?
3) The dehydrobromination of racemic 1,2-dibromo-1,2-diphenylethane was described in general terms by the following balanced equation.
Mol wt = 338 Mol wt = 56
a) The experimental procedure calls for you to use 0.588 mmol of racemic material. What mass does this correspond to?
b) What mass of KOH does the procedure require?
4) Using IR tables, to locate the absorption bands of the stretching frequencies of the alkyne C—H bond, the alkyne C=C bond, and the alkene C—H bond. Using these data, explain how you would distinguish between 1-butyne, 2-butyne and 2-butene.
Explanation / Answer
1) the boiling point of triethylene glycol is more than the boiling of given alcohols so it is used in the said elimination reaction
2) the bases are stronger if they have better affinity for H+ ions
Also the conjugate base of a weak acid is stronger as compared to conjugate base of a strong acid
Here
ethoxide ions or methoxide ions are conugate base of weaker acid (as compared to OH- which is conjugate base of H2O, stronger acid as compared to methanol and ethanol)
3) the molecular weight of the recemic = 338g / mole
one mole weighs = 338 grams
so 0.588moles will weigh = 338 x 0.588 = 198.744 grams
for reaction of one mole of the racemic we need two moles of KOH
so for 0.588moles of racemic we need = 2 X 0.588moles of KOH = 1.176 moles of KOH
the mass of 1.176moles of KOH = moles of KOH x molecular weight of KOH = 65.856grams
4) the IR peaks are
terminal alkyne (1-butyne) shows C-H stretching near 3300 cm^-1 which will be absent in 2-butyne and 2-butene
carbon-carbon triple bonds shows stretching band near 2100-22200 cm^-1 (for 2-butyen), while Alkene (C=C) stretches is observed near 1,660 cm–1 (for 2-butene).
The 2-butene will also show peak above 3000 cm^-1 and below 3100 cm^-1 due to C=C-H stretching which will be absent in 2-butyne.
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