chemfig: how to align the arrows of different schemes?

Question

I am trying to get the arrows of three different schemes aligned but would like to have text in between them, as you can see below.

Despite searching for hours, i haven't found a solution..

\documentclass[a4paper,pdftex,ngerman,12pt]{article}
\usepackage{chemfig}
\setatomsep{1.5em}
\setcrambond{1.5ex}{1pt}{2pt}

\begin{document}
\noindent \textbf{Cracken von Seitenketten in Aromaten:} 

\schemestart
\chemfig{**6([:-150]-----(-C_4H_9)-)} 
\arrow
\chemfig{**6([:-150]-----(-C_2H_5)-)} \arrow{0}[,0]\+ \chemfig{H_2C=CH_2}
\schemestop
\newline\newline

\noindent \textbf{Dealkylierung:} 

\schemestart
\chemfig{**6([:-150]-----(-C_2H_5)-)} 
\arrow
\chemfig{**6([:-150]------)}\arrow{0}[,0] \+ \chemfig{H_2C=CH_2}
\schemestop
\newline\newline

\noindent \textbf{Cracken von Olefinen:} 
\newline

\schemestart
\chemfig{CH_3-[:150]-[:-150]-[:150]-[:-150]=[:150]-[:-150]H_3C} 
\arrow
\chemfig{CH_3-[:-150]=[:150]-[:-150]H_3C} \arrow{0}[,0]\+ \chemfig{CH_3-[:150]=[:-150]H_3C}
\schemestop
\end{document}  

Answer 1

I'm sure there is a more elegant way, but a crude approach is to calculate the difference in width between each of the smaller left compounds (the first two) and the largest (the last) and add that as \hspace before the start of the smaller reactions. Showing each step:

\documentclass[a4paper,pdftex,ngerman,12pt]{article}
\usepackage{chemfig}
\setatomsep{1.5em}
\setcrambond{1.5ex}{1pt}{2pt}

\begin{document}
%Width of first
\newlength\lenfirst
\settowidth\lenfirst{\chemfig{**6([:-150]-----(-C_4H_9)-)}}
%Width of second
\newlength\lensecond
\settowidth\lensecond{\chemfig{**6([:-150]-----(-C_2H_5)-)}}
%Width of third
\newlength\lenthird
\settowidth\lenthird{\chemfig{CH_3-[:150]-[:-150]-[:150]-[:-150]=[:150]-[:-150]H_3C}}

%Difference for first
\newlength\lendelfirst
\setlength\lendelfirst{\lenthird}
\addtolength\lendelfirst{-\lenfirst}

%Difference for the second
\newlength\lendelsecond
\setlength\lendelsecond{\lenthird}
\addtolength\lendelsecond{-\lensecond}    

\noindent \textbf{Cracken von Seitenketten in Aromaten:} 

\hspace{\lendelfirst}\schemestart
\chemfig{**6([:-150]-----(-C_4H_9)-)} 
\arrow
\chemfig{**6([:-150]-----(-C_2H_5)-)} \arrow{0}[,0]\+ \chemfig{H_2C=CH_2}
\schemestop
\newline\newline

\noindent \textbf{Dealkylierung:} 

\hspace{\lendelsecond}\schemestart
\chemfig{**6([:-150]-----(-C_2H_5)-)} 
\arrow
\chemfig{**6([:-150]------)}\arrow{0}[,0] \+ \chemfig{H_2C=CH_2}
\schemestop
\newline\newline

\noindent \textbf{Cracken von Olefinen:} 
\newline

\hspace{0pt}\schemestart
\chemfig{CH_3-[:150]-[:-150]-[:150]-[:-150]=[:150]-[:-150]H_3C} 
\arrow
\chemfig{CH_3-[:-150]=[:150]-[:-150]H_3C} \arrow{0}[,0]\+ \chemfig{CH_3-[:150]=[:-150]H_3C}
\schemestop
\end{document}