Input/output characteristics of opamp circuits involving diodes (fast peak detector and sine-to-block wave converter)
This is homework, so I'll help you find answers, but not directly give such – that'd rob you of anything to learn.

How can I find the transfer functions of these circuits

Vout2/Vin
This is an opamp without feedback; i.e. an ideal opamp would act like a comparator. A TL081 will likely latch up under these conditions. It's generally the most terrible Opamp you're likely to find anywhere. Don't use it.
For the ideal opamp case, I'm sure that you can just plug in a few hypothetical voltages and see how this behaves. It's easy, don't be afraid to try.
Vout1/Vin
Not at all – the diodes make this a nonlinear system (made worse by the unfortunate of opamp model, but I assume you're assuming an ideal opamp). That doesn't mean this doesn't have a transfer function – but paired with C1, the system becomes time-variant and thus doesn't have a transfer function, as the diode's I/V curve will be biased to the difference between voltage across C1 and OA1's output voltage.
So, you've got both a frequency-dependent behaviour and an amplitude nonlinearity. Vout1/Vin hence depends on Vin's &quot;history&quot; and can't be reduced to a single curve.