Homonuclear C-C coupling is normally only observed in samples that are enriched with C. The range for one-bond J(C,C) is 50–130 Hz.  Two-bond J(C,C) are near 10 Hz.
The trends in J(H,C) and J(C,C) are similar, except that J(H,C are smaller owing to the modest value of the C nuclear magnetic moment.  Values for J(H,C) range from 125 to 250 Hz.  Values for J(H,C) are near 5 Hz and often are negative.