gHMBC

Set up appropriate ¹H parameters. Normally should acquire 1D ¹H spectrum first.

pw = ¹H pulse, should be 90º pulse

tpwr = high power for ¹H; should be set according to pw, or is correlated to pw.

nt = number of scans, should be multiple of 2, but 1 is acceptable

ni = number of t1 increments, points in t1 dimension, must be even number, normally at least 256, 350 is preferable (in VNMRJ 4.2, gHMBC does phase sensitive acquisition, so ni = 100 ~ ni = 200 in VNMR 6.1c)

np = number of points in t2 dimension, must be even number, 2048 is standard

d1 = relaxation delay; normally should be slightly longer than in gCOSY, so 1.5 seconds is normal, but aromatic (or vinyl or methyl) protons usually need 2.0-2.5 seconds for optimal signal-to-noise

Steps:

1) Acquire 1 scan of 1H 1D experiment. Set cursors ~0.5 ppm beyond last proton resonance on both sides of spectrum, type command:

movesw

2) Re-acquire 1H 1D experiment (this is only required for 1H 1D on side of 2D spectrum)

3) Move parameters to another experiment. To move parameters from experiment 1 to experiment 3 type command:

mp(1,3)

4) Change to experiment 3, type command:

jexp3

5) Set gHMBC parameters with setup macro, type command:

gHMBC

6) Spin will likely turn off, if it does not, open Acqi window and manually turn it off. Lock Level should not drop more than ~5 %-10 %. If it does, you should reshim non-spin shims- X1, Y1, XZ, and YZ, and on higher field (500/600) X2Y2 and XY

7) Set the number of scans (nt) to appropriate value, generally 1 or 2 (it is preferable for nt to be a multiple of 2; nt might need to be increased for sufficient signal-to-noise, generally nt = 2 is sufficient if decent 1H spectrum can be acquired in 8 scans), type:

nt=2

8) Set the number of points in t1 dimension (second dimension) (ni), generally 200-400 are suggested, type:

ni=256

9) Set d1 time, normally should be slightly longer than in gCOSY, so 1.5 seconds is normal, but aromatic (or vinyl or methyl) protons usually need 2.0-2.5 seconds for optimal signal-to-noise

10) Set the parameters sw1, dof, and j1xh; sw1 = spectral width in 13C dimension, the default is ~-10 to 220 ppm; if you have a 13C beyond that range then sw1 must be increased or dof (the center of the carbon spectrum must be changed); the default value of j1xh (the 1-bond 1H/13C coupling constant) is 140 Hz, which is approximately correct for aliphatic proton/carbon pairs, aromatic 1-bond 1H/13C coupling constants are 170-250 Hz, so j1xh = 180 (VNMRJ 4.2 allows for range of values for j1xh with paramaters j1min and j1max, typically set to j1min = 130 j1max 165 but you can change as appropriate for your sample)

11) Start acquisition, type command:

go

12) At end of experiment, set appropriate weighting functions and linear prediction parameters, type commands:
processhmbc

13) Spectrum should be appropriately referenced already, but you should confirm this; if necessary re-reference by putting cursor on appropriate diagonal peak and type (assuming CDCl3):

rl(7.26p)

rl1(77d)

dp10

14) Adjust vertical scale with vs +20% and vs -20% menu buttons or with middle mouse button or manually changing the parameter, vs2d, so vs2d = 100 (the lower the number, the less noise displayed), then redraw 2D with dp10 command

15) Print with full rectangle, type:

full

dp10

pcon(10,1.2) page

16) Save data, type:

svf('filename')