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Self-­‐Learn  

©  E-­‐PG  Pathshala  :  NMEICT  &  UGC  

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Module  Details  and  Tags  

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Subject Chemistry

Paper  No  and  Title Paper  12:  Organic  Spectroscopy

Module  No  and  Title Module  13:  Chemical  ShiH  and  Its  Measurement

Module  Tag CHE_P12_M13_e-­‐Text

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Developing  Team  

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Principal Investigator Co- Principal Investigator and

Technical Coordinator Prof A.K.Bakhshi

Sir Shankar Lal Professor, Department of Chemistry University of Delhi

Dr Vimal Rarh

Deputy Director, Centre for e-Learning and Assistant Professor, Department of Chemistry, SGTB Khalsa College,

University of Delhi

Specialised in : e-Learning and Educational Technologies

Paper Coordinator Content Writer Reviewer Prof Diwan S Rawat,

Professor,

Department of Chemistry, University of Delhi

Prof Diwan S Rawat, Professor,

Department of Chemistry, University of Delhi

Dr Deepak Kumar Assistant Professor,

Department of Chemistry, University of Delhi

Prof M S M Rawat

Department of Chemistry

Hemwati Nandan Bahuguna Garhwal University, Uttarakhand

Anchor  Ins4tute    :    SGTB  Khalsa  College,  University  of  Delhi  

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©  E-­‐PG  Pathshala  :  NMEICT  &  UGC  

Learning Outcomes

To  understand  the  posiMon,  intensity  and  shape  of  an  absorpMon  band     To  understand  the  shielding  and  deshielding  effect  

To  understand  the  measurement  of  chemical  shiH  value    

To  understand  the  meaning  of  equivalent  and  non-­‐equivalent  protons  

To  understand  the  meaning  of  homotopic,  enanMotopic  and  diastereotopic  

protons  

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Self-­‐Learn  

Speaker  Video  

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Self-­‐Learn  

Compared  to  a  naked  proton,  a   shielded  proton  requires  a  higher  

applied  field  strength,  whereas  a   deshielded  proton  requires  lower  

field  strength  for  transiMon.  

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Chemical  ShiB  Values  

Each  proton  in  a  molecule  is  in  a  slightly  different  

chemical  environment  and  hence  they  do  not  have  

much  difference  in  their  resonance  frequency.    

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Thus  the  chemical  shiH  value  does   not  depend  on  the  operaMng  

frequency  and  it  is  a  dimension   less.  That  is  why  chemical  shiHs  

have  been  defined  in  relaMve   terms  (δ-­‐scale),  rather  than  

absolute  terms  (hertz).  

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Speaker  Video  

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7.3  Diastereotopic  protons    

If  two  protons  are  neither  homotopic   nor  enanMotopic,  then  they  are  not   chemically  equivalent.  Consider  the   protons  on  C3  of  (R)-­‐2-­‐butanol.  These   protons  cannot  be  interchanged  by   either  rotaMonal  symmetry  or  

reflecMon/plane  of  symmetry.  

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8.  Signal  Area  

The  area  under  a  peak  in  1H  NMR  spectrum  is   proporMonal  to  the  number  of  protons  in  a  given   chemical  environment  in  a  molecule  (e.g.,  if  the  area  

under  a  peak  is  two  Mmes  the  area  under  another   peak,  there  are  twice  as  many  protons  responsible  

for  the  larger  peak  than  for  the  smaller  one).    

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Summary

Speaker  Video  

References

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