[crossfill]

I would like to ask how can I know whether the spectrum is in first order or 2nd order? Just by using the spectrum. For example, the following spectrum is given without any information. How can I know it is 1st order or 2nd order nmr spectrum?

[cundi]

A first order spectrum must have th theoretical patterns of multiplicity.

This one is, i think, 1st order.

[Dolphinsiu]

Whether the proton nmr spectrum given is 1st order or 2nd order depends on how close (dv) is the two chemical shift of the two chemically non-equivalent protons. If dv/J is greater than 10, then it is a first order situation. If dv/J is less than 10, then it is a second order situation. In second order situation, you are difficult to predict the connectivity of protons due to peak overlapping (e.g. distorted doublet, triplet etc.) seen in 1st order spectrum. For example, benzene. Hence, we would use alphabatical order to differientiate 1st order and 2nd order. For A2X2 system, it is obviously first order. For ABCD system, it is obviously second order. Is it clear?