positive Jones 6) Cirele the compound that would yield the following combination
ID: 551958 • Letter: P
Question
positive Jones 6) Cirele the compound that would yield the following combination of qualitative test: test, positive 2,4-DNP test, and negative bromine test IO OCCH3 CHO 7) The melting point ofpure urea is 132.5-133.0° C. Predict the effect of each of the following changes on the melting point of this sample. Mixing the urea with a small amount of cinnamic acid (m.p 132.5-133.0° C). (a) m.p. increases (b) m.p. decreases (c) m.p. remains the same Mixing the urea with a small amount of salicylic acid (m.p. -158.5-159.0° C). (a) m.p. increases (b) m.p. decreases (c) m.premains the same 2· The questions that follow concern the separation and analysis of the following four aromatic compounds a) A mixture containing the compounds below was separated by normal-phase thin-layer chromatography, using silica gel as the stationary phase and a 1:1 mixture of hexanes and ethyl acetate as the mobile phase. Rank the molecules below in order of decreasing Rf under these conditions. 10 pts) b) Rank the following solvents in order of eluting power: (10 pts) I) Chloroform 2) benzene 3) methanol 4) ethyl acetate 5) hexane (highest) _(lowest) c) Which compound(s) would be extracted from an organic phase into an aqueous phase containing sodium hydroxide? (3pts) d) Which compound would have the highest melting point? (3 pts)Explanation / Answer
q6) The compound E is the one which gives positive Jones test, positive 2,4-DNP test and negative bromine test.
JOnes oxidation - oxidation of primary/ secondary alcohols / aldehydes with chrmium trioxide .
Thus only compound that gives Jones test is benzaldehyde E
All carbonyl compounds (ketonesand aldehydes ) give positive 2,4- DNP test .
Aromatic compounds do not give bromine test , only unsaturated compounds (alkenes and alkunes 0 give positive bromine test.
7) When we mix an impurity into a substance the m.p. is lowered. The mixture melts at a lower temperature than either of the component.
Thus in both
a) and b) the answer is m.p. is decreased.
8)In general , the less polar is the compound , the fast it moves on TLC thus has higher Rf
Thus the order of decreasing Rf is
K > P > N > M > L
K is a halide , P ester , N a ketone , M an alcohol and L is carboxylic acid
b) The more polar solvents are more powerful eluters. Thus the elution power is rougly the order of polarity of solvents.
methanol >ethyl acetate > chloroform > benzene > hexane
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