Due to steric restrictions, this torsion angle usually is present as gauche- or gauche+ rotamers. The epsilon (e) torsion angle can be derived from the ³J_P3'-H3',  ³J_P3'-C2' and ³J_P3'-C4' coupling constants. In particular:

J(H3'-O-C-P)=15.3cos²(e+120)-6.2cos(e+120)+1.5

For trans ang gauche conformations, ³J_P3'-H3' is similar (5 Hz)

³J_P3'-C2' and ³J_P3'-C4' can be used to distinguish between the two conformers: ³J_P3'-C4' is large for trans and small for gacuhe-, while the opposite behvior is expected for ³J_P3'-C2'

Some methods to measure them are:

• J_PH
• ¹H-Selective 2D ³¹P J-resolved experiment ( 87JACS7525 )
• 91QRB479
• 94JB595
• P-FIDS-CT-HSQC experiment ( 93JB479 and 94JB631 ).
• 95JB315
• 2D constant-time 1H-1H {31P} COSY experiment using quantitative J-correlation spectroscopy ( 98JMR164-134 )
• From CT-HMQC-J experiment ( 99JMR181-139 )
• From ¹H-¹³C HSQC experiment ( 92NAR4747 , 96JMRB59-113 )
• From 2D band-selective TOCSY experiment ( 96JMRB46-113 )
• 2D {³¹P} Spin-Echo Difference CT [¹H-¹³C]-HMQC experiment ( 99JMR491-140 ).
• 2D ¹H-³¹P F1-J-scaled HMBC experiment ( 00MRC692 ).
• 2D CT-NOESY ³¹P difference experiment ( 01JB367-19 ).
• 2D and 3D PH-constant time heteronuclear COSY sequences ( 02JB65-22 )
• J_CP
• P-FIDS-CT-HSQC experiment ( 93JB479 and 94JB631 ).
• Quantitative evaluation of a 3D HCP experiment ( 98JB223 ).
• Intensity analysis in ³¹P spin-echo difference CT-HSQC ( 95FEBS156 , 97JACS7277 ), ³¹P spin-echo difference CT-HMQC ( 99JMR491-140 ), ³¹P spin-echo difference CT-HCCH ( 98JB423 ) experiments
• From ¹H-¹³C HSQC experiment ( 92NAR4747 , 96JMRB59-113 )