Chemmacros: Adjusting the properties of the coupling constant J

Question

I am working with the package chemmacros and using its convenient experimental environment to typeset my data and it works perfectly fine. However I would like to adjust the way the coupling constants J are displayed. There are three things I would like to change:

1. The coupling nuclei are displayed in italics, I would like to have upright nuclei.
2. They are displayed in brackets, but I would like to have them as a subscript.
3. The number of the bonds between the coupling nuclei n is displayed as a superscript before the J. Unfortunately, the distance between the J and this number n is too large. Is there a way to make it smaller?

Here is my MWE:

    \documentclass[a4paper,10pt,bibliography=totoc,listof=totoc]{scrreprt}
    \usepackage{chemmacros}
    \usepackage{siunitx}
    \chemsetup[nmr]{delta=(ppm),pos-number=side,use-equal,format = \bfseries,list=true}       
    \sisetup{separate-uncertainty,per-mode=symbol,detect-all,range-phrase=--}

    \begin{document}
    \begin{experimental}

    \NMR(400)[C6D6] \val{2.01} (d, \J(2;CH)[Hz]{25.0}, \#{24},  \pos{5})

    \end{experimental}
    \end{document}

Thank you for your help!

Answer 1

As I already said in the comments: this is only possible by redefing an internal macro at the moment:

\documentclass[a4paper,10pt,bibliography=totoc,listof=totoc]{scrreprt}
\usepackage{chemmacros}
\usepackage{siunitx}
\chemsetup[nmr]{delta=(ppm),pos-number=side,use-equal,format = \bfseries,list=true}       
\sisetup{separate-uncertainty,per-mode=symbol,detect-all,range-phrase=--}

\ExplSyntaxOn
\cs_set_protected:Npn \__chemmacros_nmr_coupling:w (#1;#2)
  {
    \tl_set:Nn \l__chemmacros_nmr_coupling_bonds_tl { #1 \! }
    \tl_set:Nn \l__chemmacros_nmr_coupling_nuclei_tl
      {
        \c_math_subscript_token
          { \chemmacros_chemformula:n { #2 } }
      }
    \__chemmacros_nmr_coupling_aux_i:w
  }
\ExplSyntaxOff

\begin{document}
\begin{experimental}

\NMR(400)[C6D6] \val{2.01} (d, \J(2;CH)[Hz]{25.0}, \#{24},  \pos{5})

\end{experimental}
\end{document}