I have the following problems:
in the first reaction scheme the arrow is too high and I would like to bring it a little down.
in the second reaction scheme the third chemical structure (after the arrow) is a little bit low and I would like to bring it up.
in the third structure I would like to connect A to C not to B.
Thanks a lot.
\documentclass[12pt,doublespacing,letterpaper]{report}
\usepackage{chemfig}
\begin{document}
\setatomsep{2em}
\setbondoffset{1pt}
\setdoublesep{3pt}
\setbondstyle{line width=1pt}
\schemestart[0,1.2,thick]
\chemfig{R_3B}
\+
\chemfig{CH_2=CH-C(=[:90]O)-CH_3}
\arrow{%
->[\footnotesize H$_2$O]%
[]%
}[,2,thick]
\chemfig{R-CH_2-CH-C(=[:90]O)-CH_3}
\schemestop
\bigskip
\schemestart[0,2,thick]
\scriptsize\chemfig{[:-30]*6(-=-(-[,1.2]BF_3K)=-=)}
\arrow{0}[,0]\+{1em,1em ,17pt}
\scriptsize\chemfig{HO-[:75,,2](-[:115])(-[:150])-(-[:65]OH)(-[:-45])-[:-90]}
\arrow{%
->[\footnotesize SiO$_2$]%
[\footnotesize H$_2$O]%
}
\scriptsize\chemfig{*6(-=-(-[,1.1]B?-[:60,1.1]O-[:10](-[:60])(-[:20])-[:-60](-[:45])(-[:-5])-[:-145]O-[:-195]?)=-=-)}
\schemestop
\bigskip
\scriptsize\chemfig{*6(-=-(-A(-[:90]B*5(-C-*6(-=-=-)=-D=))-[:-30,1.2]OEt)=-=)}
\end{document}