J耦合谱分析以及偶极耦合课件.ppt

J耦合谱分析以及偶极耦合课件,J coupling,J耦合谱分析以及偶极耦合课件,Spin-spin Coupling,dipole-dipole interaction： magnetic dipole interaction between nuclei directly Spin-spin Coupling： It will occur between two magnetically active nuclei that are connected through chemical bonds. We can see it for two atoms directly connected, or for atoms that see one another across several bonds. Couplings are perhaps the most important parameter in NMR, as they allow us to elucidate chemical structure.,J耦合谱分析以及偶极耦合课件,Example,Ethanol: CH3CH2OH Three singlets,The spectrum is a result of spin-spin coupling (scale coupling),J耦合谱分析以及偶极耦合课件,J Coupling,Each nucleus act as a small magnet and will affect the magnetic moment of the other nuclei nearby (The energy levels of a nucleus will be affected by the spin state of nuclei nearby). The two nuclei that show this are said to be coupled to each other. The two nuclei couple leading to splitting of the two lines associated with each nucleus. Note that the interaction is mutual, and the same splitting is observed for both resonances. A splitting of a signal means that we have more energies involved in the transition of a certain nuclei. The strength of the coupling is called the coupling constant, J separation between the multiplet lines. IA and IX are the nuclear spin vectors which are proportional to mA and mB, the magnetic moments of the two nuclei. JAX is the scalar coupling constant. It does not matter if we have a 60, a 400, or an 800 MHz magnet. The coupling constants are always the same!,J耦合谱分析以及偶极耦合课件,J Coupling,The resonance frequency of Ha depends on whether the adjacent Hb has spin up or down. The frequency separation betweenthe two peaks is called J(scalar coupling constant) (typically 0 15 Hz). The coupling constant is independent of Bo and is reported in Hz.,J耦合谱分析以及偶极耦合课件,J Coupling,The resonance frequency of Ha depends on whether the adjacent Hb has spin up or down. The frequency separation betweenthe two peaks is called J(scalar coupling constant) (typically 0 15 Hz). The coupling constant is independent of Bo and is reported in Hz.,J耦合谱分析以及偶极耦合课件,Example,Ethanol: CH3CH2OH,Spin-spin coupling tells us how many nuclei there are near to a given nucleus.,J耦合谱分析以及偶极耦合课件,J Coupling,J耦合谱分析以及偶极耦合课件,J Coupling,Pascal Triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1,J耦合谱分析以及偶极耦合课件,J Coupling,If a proton interacts with two different sets of equivalent protons, the multiplicity will be: spin system, AnMmXp (m+1)(p+1) Consider CH3CH2CH2I H = 1.02; H = 1.86; H = 3.17 -CH3; 1:2:1 triplet (from methylene CH2) -CH2; quartet of triplets 12 lines (3+1)(2+1) -CH2; 1:2:1 triplet (from methylene CH2),Coupling between Sets of Spins:,J耦合谱分析以及偶极耦合课件,J Coupling,Factors affect the size of J :,The numbers of bonds involved The dihedral angle,for vicinal protons The configurations The conformations,Karplus Equation,J couplings provide an estimation of molecular conformation!,J()=Acos2() + Bcos() + C,A, B, and C are empirically derived parameters.,J耦合谱分析以及偶极耦合课件,A1 = E4 - E2 = nA - 1/2 JAX A2 = E3 - E1 = nA + 1/2 JAX X1 = E2 - E1 = nX - 1/2 JAX X2 = E4 - E3 = nX + 1/2 JAX,J Coupling,When B0 paralells Z, the H of the system is:,Analysis of spin-spin coupling:,H= - A IAz - X IXz+ JAX IA IX,m=1,H= - A IAz - B IXz + JAX IAz IXz,E4 = 1/2 nA + 1/2 nX + 1/4 JAX E3 = 1/2 nA - 1/2 nX - 1/4 JAX E2 = - 1/2 nA + 1/2 nX - 1/4 JAX E1 = - 1/2 nA - 1/2 nX + 1/4 JAX,B核跃迁频率,A核跃迁频率,J耦合谱分析以及偶极耦合课件,J Coupling,Analysis of spin-spin coupling:,J耦合谱分析以及偶极耦合课件,Analysis of 1st Order Systems,Ethylacetate (CH3COOCH2CH3) :,Nuclei A is coupled to n identical nuclei X (of spin 1/2), A will show up as n + 1 lines in the spectrum.,Since we have the same probability of finding the system in any of the states, and states in the same rows have equal energy, the intensity will have a ratio 1:2:1 for the CH3, and a ratio of 1:3:3:1 for the CH2.,Pascal Triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1,J耦合谱分析以及偶极耦合课件,In a spin system in which we have a certain nuclei coupled to more than one nuclei, all first order, the splitting will be basically an extension of what we saw before. Say that we have a CH (A) coupled to a CH3 (M) with a JAM of 7 Hz, and to a CH2 (X) with a JAX of 3 Hz. We basically go in steps. First the big coupling, which will give a quartet: Then the small coupling, which will split each line in the quartet into a triplet: This is called a triplet of quartets (big effect is the last).,Analysis of 1st Order Systems,J耦合谱分析以及偶极耦合课件,Lets finish our analysis of 1st order system with some pretty simple rules that we can use when we are actually looking at 1D 1H spectra. To do that, say that again we have a system in with a CH (A) coupled to two CHs (M and R) with a JAM of 8 Hz and JAR of 5 Hz, and to a CH2 (X) with a JAX of 6 Hz: The first rule is that if we have a clear-cut first order system, the chemical shift of nuclei A is always the center of the multiples. The second one is that no matter how complicated the pattern may end up, the o。