documentclass[10pt,a4paper]{article}
usepackage[utf8]{inputenc}
usepackage{amsmath}
usepackage{amsfonts}
usepackage{amssymb}
usepackage[left=0.00cm, right=0.00cm]{geometry}
usepackage{tikz}
usepackage{chemfig}
usepackage{mhchem}
usetikzlibrary{calc,fadings,decorations.markings}
begin{document}
    begin{tikzpicture}
        setchemfig{atom sep=2em}
        % ---------------- LABELS ----------------
        node[align=center] (alkyne) at (0,0) {Alkyne\{{footnotesize chemfig{-C~C-}}}};
        node[align=center] (haloalkene) at (2,3) {Haloalkene};
        node[align=left] at (3.65,3) {{footnotesize chemfig{C(-[:-120])(-[:120]R)=C(-[:60]X)-[:-60]}}};
        node[align=center] (haloalkane) at (0,6) {Haloalkane};
        node[align=left] at (1.8,6) {{footnotesize chemfig{-C(-[:90]R1)(-[:-90]R2)-C(-[:90]X)(-[:-90]R3)-}}};
        node (alkane) at (-1,3) {Alkane};
        node at (0.2,2.7) {footnotesizechemfig{-C(-[:90]H)(-[:-90]H)-C(-[:90]H)(-[:-90]H)-}};
        node (tertiaryalcohol) at (0,8) {3$^circ$ Alcohol};
        node (alkene) at (-3.2,3) {Alkene};
        node (ketone) at (-4,0.4) {Ketone};
        node (alcohol) at (-6,3) {Alcohol};
        node (glucose) at (-6,6) {Glucose};
        node (ester) at (-6,-1) {Ester};
        node (carboxylicacid) at (-9,1) {Carboxylic Acid};
        % BOXES FOR PRIMARY (1 DEGREE) AND SECONDARY (2 DEGREE) ALCOHOL
        draw[-latex] (alcohol) -- (ketone);
        draw[fill=white] (-6.5,2.3) rectangle (-6,2.8) (-6,2.3) rectangle (-5.5,2.8);
        node at (-6.25,2.55) {1$^circ$};
        node at (-5.75,2.55) {2$^circ$};
        % ---------------- ARROWS ----------------
        draw[-latex] (alkyne) -- node[above,midway] {ce{HX},ce{X2}} node[below,midway] {halogenation} (haloalkene); % HOW DO I ROTATE THE LABELS ABOVE AND BELOW THE ARROWS HERE
        draw[-latex] (haloalkene) -- (haloalkane);
        draw[-latex] (alkyne) -- (alkane);
        draw[-latex] (alkane) -- (haloalkane);
        draw[-latex] (alkene) -- (alkane);
        draw[-latex] (alkyne) -- (ketone);
        draw[-latex] (alcohol) -- (haloalkane); % HOW DO I DRAW THE REVERSE ARROW HERE
        draw[-latex] (haloalkane) -- (tertiaryalcohol);
        draw[-latex] (alkene) -- (haloalkane);
        draw[-latex] (alcohol) -- (alkene); % HOW DO I DRAW THE REVERSE ARROW HERE
        draw[-latex] (glucose) -- (alcohol);
        draw (alcohol) -- (ester); % HOW DO I ADD THE CURLY BRACKETS AT THE ALCOHOL AND HOW DO I ADD THE EQUILIBRIUM REACTION ARROW AT THE KETONE END
        draw (carboxylicacid) .. controls +(0:3) and +(90:2) .. (ester);
        % ---------------- ADDITIONAL DECORATIONS ----------------
        draw[-latex] (glucose) .. controls +(-90:1) and +(180:1) .. (-5,5) node[right] {ce{CO2}};
    end{tikzpicture}
end{document}