Use HoldForm applied to each fraction to keep the fractions from combining.
HoldForm[1/2] HoldForm[3/4]
to produce $$ \frac{1}{2} \frac{3}{4} $$
or
HoldForm[(1/2) (3/4)]
to produce $$ \frac{3}{2 \times 4} $$
Using TeXForm produces the desired LaTex code.
(HoldForm[1/2] HoldForm[3/4]) // TeXForm
(* \frac{1}{2} \frac{3}{4} *)