Map Branched molecules tend to have a greater friction coefficient than a shorte
ID: 530051 • Letter: M
Question
Map Branched molecules tend to have a greater friction coefficient than a shorter more compact molecule. Which of the molecules below will have the greater electrophoretic mobility? COO O Same mobility COO OOC Electrophoresis is run at pH 9.0 on a capillary tube with the detection end negative and the injection end positive. The electroosmotic flow from the positive end to the negative end is greater than the electrophoretic flow. Which molecule would elute first? O Same time Electrophoresis is run at pH 2.0 where the electroosmotic flow is weak. The detection end is positive and the injection end is negative in this setup. Which molecule would elute first? O Same timeExplanation / Answer
In the case of electrophoresis, there will be a layer of oppositely charged ions (or dipole) around the molecules. The molecules/ions will move in the opposite direction of that of the analyte molecule. In our case, molecule A is trans and it is symmetrical. Thus the effect of solvation (or the layer formed) formed will be same at both the ends (opposite). Whereas in the case B, both the carboxylic acids are on the same side and the interaction between the analyte and the layer will be high. Thus it moves slowly. A
B). At PH 9 the molecules exist as carboxylic ions, as discussed earlier A will elute first. Since the carboxylic groups are in opposite direction
C). At PH 2 the molecule is not charged, they exist as carboxylic acid. Since the detection end is positive B will be detected first. Since permanent dipole moment of the molecule, A is smaller than that of B, due to the orientation of carboxylic groups. (In trans case carboxylic groups are oriented in opposite direction and the dipole moment will cancel each other)