Name _________________________ Exam 3, 2009: CHEM/BCMB 4190/6190/8189 1 Exam 3: CHEM/BCMB 4190/6190/8189 (114 points) Thursday, 29 October, 2009 1). For a simple two spin (1H-13C) coupled system (i.e. 13CHCl3), the population diagram is shown (below, right). Here “H1” and “H2” represent the 1H transitions, and “C1” and “C2” represent the 13C transitions. We’ll consider the effect of the pulse sequence shown (below, left) assuming the Larmor frequency is equal to the reference frequency (±L=±ref). Assume ²=1/(4J) and ignore the effects of magnetic field inhomogeneity. a. What is the name of the pulse sequence shown. If it is an acronym, state what the acronym stands for? (2 points) INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) b. Complete the vector diagrams below for points ‘c’, ‘d’, ‘e’, and ‘f’ in the pulse sequence. Be sure to label the vectors (MHC³, MHC´), to include arrows indicating the direction of precession for the vectors in the rotating frame, and to indicate the angle (µ)between the vectors at each point. In this example, the precession frequency of MHC´is slightly faster than the Larmor frequency. (8 points) e ²a b c d f g 90x180x90y 180x90x 13C ²1H g¶h 1H 13CN2N1N3N4C1³´´³³³´´C2H1H2x µ= 0° MHC´MHC´MHC³transverse planey z x 90°xy x ²MHC³MHC´x µ= 90° y a b c 180°x 1H MHC´MHC³µ= 90° y 180°x 13C ²MHC³MHC´µ= 180° x y d e f x MHC³MHC´µ= 90° y MHC³
This preview has intentionally blurred sections.
Sign up to view the full version.
Name _________________________ Exam 3, 2009: CHEM/BCMB 4190/6190/8189 2 c. Which of the hydrogen transitions, H2(N1-N3) or H1(N2-N4) corresponds to MHC±? (2 points) H2d. Draw the vector diagram showing the MHC±and MHC²vectors at point ‘g’ in the pulse sequence. Make sure to label each vector (MHC±, MHC²). (4 points). e. Ignoring the effects of relaxation and magnetic field inhomogeneity, write down the populations of the states N1, N2, N3and N4at each point to ‘g/g³’ in the sequence. The values at equilibrium (at point ‘a’) are given below (note: point ‘d’ is following the 1H 180°x pulse, and ‘e/f’ is, subsequently, following the 13C 180°x pulse). (8 points) ‘a’ ‘b/c’ ‘d’ N4= N N4= N + ´H/2 N4= N + ´H/2 N3= N + ´C N3= N + ´C + ´H/2 N3= N + ´C + ´H/2 N2= N + ´H N2= N + ´H/2 N2= N + ´H/2 N1= N + ´C + ´H N1= N + ´C + ´H/2 N1= N + ´C + ´H/2 ‘e/f’ ‘g/g³’ N4= N + ´H/2 N4= N + ´H N3= N + ´C + ´H/2 N3= N + ´C N2= N + ´H/2 N2= N N1= N + ´C + ´H/2 N1= N + ´C + ´H MHC²MHC±y z x g