What software was used to create these organic reaction scheme figures?
$\mathrm\LaTeX$ to the rescue
I reproduced these reaction schemes with $\mathrm\LaTeX$ using the following particular packages:

chemfig for drawing 2D chemical structures (note that I enabled sans-serif font for the labels like the original did);
chemmacros for the typesetting of chemical formulas and chemistry-related notations;
siunitx for handling physical quantities (here, temperatures);
stix for loading STIX fonts, which in my opinion are the best choice for technical writing due to canonical and coherent appearance of the glyphs and great coverage for special symbols.

All of this is free for any type of use, works on all major operating systems used in production and the source code is available.
Result

Source code
% !TEX program = pdflatex

\documentclass{report}
\usepackage[T1]{fontenc}
\usepackage{stix}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{siunitx}
\usepackage{chemmacros}
\chemsetup{
    modules = all,
}

\newcommand{\bndlen}{1.7em} 
\newcommand{\bndlenshort}{0.5}
\newcommand{\bndlenshorter}{0.75}
\newcommand{\bndlenlonger}{1.5}
\newcommand{\bndlenlong}{1.75}
\newcommand{\lnwidth}{0.8pt}
\newcommand{\cramwid}{0.3em}

\usepackage{chemfig}
\setchemfig{
    angle increment = 15,
    atom sep = \bndlen,
    bond offset = 1pt,
    double bond sep = 3pt,
    cram width = \cramwid,
    compound sep = 5.0em,
    arrow coeff = 1,
    arrow offset = 12pt,
    scheme debug = false,
    bond join = true,
    chemfig style={line width=\lnwidth},
    arrow style={line width=\lnwidth},
}
\renewcommand*\printatom[1]{\ensuremath{\mathsf{#1}}}

\begin{document}

\schemestart
    \chemfig{MeO-[::30]*6(-=-(-~--[::-60]CHO)=-=)}
    \arrow{-&gt;[\parbox{5cm}{\centering
        i) \ch{Hg^2+}, dil.~\ch{H2SO4}\\
        ii) \ch{AgNO3}, \ch{NH4OH}
    }][
        iii) \ch{Zn}-\ch{Hg}, conc.~\ch{HCl}]}[,2.5]
    \textbf{Q}
    \arrow{-&gt;[\parbox{5cm}{\centering
        i)~\ch{SOCl2}\\
        \hphantom{i)~}pyridine
    }][
        ii) \ch{AlCl3}]}[,1.5]
    \textbf{R}
    \arrow{-&gt;[\parbox{5cm}{\centering
        \ch{Zn}-\ch{Hg}\\
        conc.~\ch{HCl}
    }]}[,1.5]
    \textbf{S}
\schemestop

\bigskip

\schemestart
\chemfig{(-[::120]*5(---=-))-~-(-[::-60]*6(---=--))}
\arrow{-&gt;[
        i) \ch{H2}, \ch{Pd}-\ch{BaSO4}, quinoline
    ][
    ii) dil.~\ch{KMnO4}~(excess), \SI{273}{\kelvin}]}[,3.5]
\textbf{P}
\schemestop

\bigskip

\schemestart
    \chemfig{H_3C-[::-30](-[::-60]Br)-[::60]-[::-60]Br}
    \arrow{-&gt;[\parbox{5cm}{\centering
        i) alc.~\ch{KOH}\\
        ii) \ch{NaNH2}
    }][
        iii) red hot iron tube, \SI{873}{\kelvin}]}[,3]
\schemestop

\end{document}