Methanoic acid with chemfig? (molecule with labels(nodes) of angles, bonds and bondlength)

Question

I want to use chemfig for my academic work - but I have a lot of problems. I have found something as my inspiration to write this code.

\documentclass[12pt,a4paper,onecolumn]{article}
\usepackage{chemfig}
\usepackage{tikz}   

\begin{document}
\begin{tikzpicture}   
\path node(A){\chemfig{
@{H1}H-[@{HB1}:30]@{C1}C(=[@{CDB1}:90]@{O1}O)-[@{CB2}:-30]@{O2}O-[@{OBH1}:30]@{H2}H
}};
\chemmove{
\draw (HB1) node[above] {$\alpha$};
\draw (CDB1) node[right] {$\beta$};
\draw (CB2) node[above] {$\gamma$};
\draw (OBH1) node[above] {$\zeta$};
\draw (CB2) node[above] {$\gamma$};
\draw (C1) node[below] {$\theta_A$};
\draw (O2) node[above] {$\theta_b$};
}
\end{tikzpicture} 
\end{document}

But I am still far from what I would like to have.

Wishes

• Drawing the two red arrows to show where the angles are.
• Replacing Alpha to Zeta with a to d. Problem: the letters are too big. I would like to have them tiny (didn't worked). I would like to have them in grey. And it would look nice if they could rotate - they should (if possible) have the same rotation as the bonds they show to.
• The "thetas" are too big. I would like to have the smaller. And they are too close to the letters C and O. And it would be nice if they could have the two red arrows around to show that they are angles.
• Using the correct angles to draw the molecule. Theta_A has an angle of 112, while Theta_B has an angle of 110. All in degrees.
• In the GIMP figure the size is really bad. The letters (not the molecule letters) are too big (in my opinion) in proposition to the bonds. But I think if you could make the letters smaller it would look nice?

Kind regards! And thank you very much in advance!

PS! The picture frame is nothing that should be written in LaTeX. It was just to show you the molecule in a fancy way.

Answer 1

With the help of Section 12.7 of the chemfig manual I was able to get something that should be close. The distance between atoms can be changed with \setatomsep, and font colors, sizes, etc. can be modified as per usual TikZ commands.

\documentclass[border=2pt]{standalone}
\usepackage{chemfig}
\usepackage{siunitx}

\newcommand\namebond[5][-1pt]{\chemmove{\path(#2)--(#3)node[midway,#4,yshift=#1,black!60]{#5};}}
\newcommand\arcbetweennodes[3]{%
\pgfmathanglebetweenpoints{\pgfpointanchor{#1}{center}}{\pgfpointanchor{#2}{center}}% 
\let#3\pgfmathresult}

\newcommand\arclabel[6][red,-stealth,shorten <=1pt,shorten >=1pt]{%
\chemmove{%
\arcbetweennodes{#4}{#3}\anglestart \arcbetweennodes{#4}{#5}\angleend \draw[#1]([shift=(\anglestart:#2)]#4)arc(\anglestart:\angleend:#2); \pgfmathparse{(\anglestart+\angleend)/2}\let\anglestart\pgfmathresult \node[shift=(\anglestart:#2+1pt)#4,anchor=\anglestart+180,inner sep=0pt,
outer sep=0pt]at(#4){#6};}}

\begin{document}
\setatomsep{2cm}
\chemfig{@{hl}H-[:34]@{c}C(=[:+90]O@{ot})-[::+-56]@{ob}O-[::55]@{hr}H}
\namebond{hl}{c}{above,sloped}{$a$}
\namebond{c}{ot}{right}{$b$}
\namebond{c}{ob}{above,sloped}{$c$}
\namebond{ob}{hr}{above,sloped}{$d$}
\arclabel{0.5cm}{hl}{c}{ob}{\footnotesize \SI{112}{\degree}}
\arclabel{0.5cm}{c}{ob}{hr}{\footnotesize \SI{110}{\degree}}
\end{document}