Magnetic Shielding

University:
Swansea University
Course:
PM134 | Microbiology
Academic year:

2023
Views:

47

Pages:

3
Author:

Amal J.

0U1Magnetic ShieldingCH3COOH spatiumpeak due toProtons surrounded by electrons thatpeak due toCH3OHshield them from external field.8 ppmcircularing elections create an inducedmagnetic field that opposes the extunal field (magnetic)Depending on the chemical environment prolons in a moleculeare shielded by different amounts.H(more Shielded,absorbs atH O:/higher field)HH ( less shielded, absorbs at lower feld)EM. radiationDifferent hucri absorb different wavelength.Nuclei of given typewill resonate at different energiesdepending on their chemical and electronic environment The position (chemical shift S) E pattern (splilling or multiplicity)of the NMR signals gives imp info about the chemical environment ofthe nuclei.chemical shift ( 8)shilding Ey deshielding effect causes the change in theeffective field on the nuclear spin and thus cause the NMRfrequency to shift The frequency of absorption for a nucleusof interest relative to the frequency of absorption of a molecularstandard is called chemical shift of the nucleusIf a protein absorbs at 60 Hz in a GOMHL instrument.S = 60x106160x106ppm8= [vo(H) - Vo (TMS)]Spectrometer frequency in MHZ]iHOFNMe,Si(TMS)HeM-RhC(N)s3Ho302010O-108ppm most protons fall in this. regionDannieldBodicuases Field sweep Bo correasesDownshieldedupfieldVo increases Frequency surep vo decreases shieldedHigh frequencylaw frequency 1. Spin- - Spin coupling is dependent upon the no. of equivalentprolons on the adjacent Carbon. It is an indirectcouptingof nonequivalent protons on adjacent carbons havingmagneticfields that may align with or oppose the external fieldMagnetic coupling causes the proton to absorb slightly downfieldwhen the external field is reinforced of Slightly upfield whenthe extural field is opposed. All possibilities exist, so signalis split.A+1 rule:-Ha Set of hydrogens has n neighbouring , non-equivalent hydrogers,it will be Split into n+1 Subpeaks.splitting occurs primarily between hydrogens that are separated by3 bonds. Spin - spin coupling effect is quantified by couplingConstant (J). The coupling constant is the difference expouredin Hx between two adjacent Sub-peak in a spect signalOne prolon on an adjacent carbon will sput a proton intoa doublet , 2 peaks of 1: relative intensity. 2 proton on a4adjacent Carbon will Spitt into triplet 3 peaks of 1:2:relative intensity. 3 prolon on a adjaced carbon will splitintoquarter (q,) 4 peaks of 1:3:3:1 relative intensityEquivalentnvatani do not show Sinin - spin coulina.