Problem with alignment

Question

I have the following tikz code:

\schemestart
  \chemname{\chemfig[][scale=0.6]{
    *6(-=(-\lewis{6,O}-[:30]*6(-(=\lewis{57,O})(-[90,0.25,,,draw=none]@{a1}S)-\lewis{26,O}*6(--)))-=-*6(-(=\lewis{13,O})-(*6(-=-=-=)))=)
  }}{
    2-(4-benzoylphenoxy)essigsäure Ethylesther
  }
  \chemfig{
    \chemsign{+}
@{a0}\vphantom{K}\chemabove{K}{\hspace{5mm}\scriptstyle\oplus}
\hspace{4mm}
\chemabove{OH}{\hspace{-7mm}\scriptstyle\ominus}
  }
  \chemmove[-stealth,red,shorten <=3pt]{
    \draw(a0)..controls+(up:10mm)and+(north west:10mm)..(a1.north);}
  \arrow
  \arrow(@c1--){0}[-90,0.333] % Line break!
  \chemname{\chemfig[][scale=0.6]{
    *6(-=(-O-[:30]*6(-(-[:330]\Lewis{15,O}-[:330]-[:30]O)(-[:210]\Lewis{357,O})-OH))-=-*6(-(=O)-(*6(-=-=-=)))=)
  }}{
    2-(4-benzoylphenoxy)essigsäure
  }
  \chemfig{
    \chemsign{+}
\chemabove{K}{\hspace{5mm}\scriptstyle\oplus}\hspace{4mm}
\chemsign{+}
H_2O
  }
  \arrow
\schemestop

This gives this image:

It is easy to see that the added K^(+) and (+)^OH are not aligned correctly. I tried it with \vphantom{K} but it doesn't seem to work.

One strang thing is also the red arrow. In my original document he isn't pointing at the right location, but using standalone for producing this image resulted in the correct arrow position. What can be the reason for that?

Answer 1

I usually don't use \chemname and \chemsign within the \schemestart \schemestop “environment”. (But that may be personal preferences). Instead I often use invisible arrows with length zero for dividing compounds. Also, I'd choose more meaningful node names than the default c1, c2,... This way it's easier to see when you refer to a compound which one you actually mean and it doesn't matter if the automatic names change due to changes to the whole scheme.

Since I also don't like \oplus and \ominus for formal charges I'd use (my own) chemmacros which provides macros for them, e.g. \fplus and \fminus. Its \ch macro also allows for much easier syntax when you try to input ions, especially ones with formal charges.

All in all I'd do something like this (while playing with the code I changed details in the skeleton formulas and was too lazy to undo them again...):

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{chemfig}
% formal charges and other stuff like the \ch{} macro:
\usepackage{chemmacros}

\begin{document}

% turn all of chemmacros' charges into formal ones,
% i.e. also the ones set with \ch{}:
\chemsetup{option/circled=all}

% the scheme:
\schemestart
  \setatomsep{1.8em}
  \chemfig{
    *6(
      -=(
        -\lewis{26,O}-[:30]*6(
          -(=\lewis{57,O})-[@{a1,0}]\lewis{26,O}*6(--)
        )
      )-=-*6(-(=\lewis{13,O})-(*6(-=-=-=)))=
    )
  }
    %
  \arrow(ester.-5--){0}[,0]
  \ch{+ K+}%
  \chemfig{
    @{a0}{\ch{^-OH}}
  }
  \chemmove[-stealth,red,shorten <=1pt, shorten >=3pt]{
    \draw(a0)..controls+(up:10mm)and+(up:10mm)..(a1.north);}
  \arrow
  \arrow(@ester--estername){0}[-90,.2] longuncomprehensiveiupacname
  \arrow(@estername--saeure){0}[-90,0.333] % Line break!
  \setatomsep{1.8em}
  \chemfig{
    *6(
      -=(
        -O-[:30]*6(
          -(-[:330]\lewis{15,O}-[:330]-[:30])(-[:210]\chembelow[1.5ex]{\lewis{357,O}}{\fscrm})-OH
        )
      )-=-*6(-(=O)-(*6(-=-=-=)))=
    )
  }   
  \arrow(.-6--){0}[,0]
  \ch{+ K+}
  \arrow
  \arrow(@saeure--){0}[-90,.2] longuncomprehensiveiupacname
\schemestop

\end{document}