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# Coupling constant

Learn how to predict splitting patterns based on the molecular structure, and how to find coupling constants from the peaks in a multiplet by using roofing to figure out which protons are splitting each other. Created by Jay.

## Want to join the conversation?

• At , how do you know that the red proton is attributed to the peak with the lower chemical shift than the blue proton which has a peak with a higher chemical shift?
• I'm not entirely sure, but I think that this is the case because the blue proton is closer to the OSi(Me)3 group which is electronegative, thus it is more deshielded and experiences a higher magnetic field and thus a higher chemical shift. It is relatively closer to the OSi(Me)3 group because it is cis to it rather than the other hydrogen which is trans.
• At : Did you determine the distance between the peaks by adding the two peak numbers together, so 4 + 3 = 7? Or was it determined in another way with a scope outside of this video?
• Coupling constants are values that must be memorized (or will be provided) and depend on the relative position of protons and their near neighbors. These are independent of the number of peaks, and 3+4=7 was just a coincedence
• I don't understand how the two hydrogens are chemically different. Can someone explain this to me more in depth? Is it only when there is a double bond?
(1 vote)
• No, it's not only when there is a double bond.
Two hydrogens are chemically different if, when you replace them separately with an X group, to get a different compound.
In CH₃CH₂CH₃, replacing an H with X on C1 or C3 gives CH₃CH₂CH₂X, so those six H atoms are chemically identical
Replacing one of the H atoms on C2 gives CH₃CHXCH₃, so those two H atoms are chemically identical but chemically different from the other six H atoms.
• so if there was rotation about the double bond, the protons would be equivalent?
• Yes they would be equivalent if they could rotate
• What is J-coupling?Or more importantly the differences between 1-2-3?
• at
why we use Hz as a unit of coupling constant ? this video says that it is because of different spectrometer's frequency, but even with different spectrometer frequency we still can calculate the same chemical shift δ right ?
• We use δ for chemical shift because the frequency varies with spectrometer frequency.
We use Hz for coupling constant because it is a constant.
If J = 7 Hz on one spectrometer, it is the same on every spectrometer.
• Hello,
is there any way to determine the coupling constant from the spectrum? or has it to be given?
could you please explain me what is the difference between the spectrum of first order and higher ones?
Thank you :)