Laravel 4 Eloquent Query Using WHERE with OR AND OR?

Make use of Parameter Grouping (Laravel 4.2). For your example, it'd be something like this:

Model::where(function ($query) {
    $query->where('a', '=', 1)
          ->orWhere('b', '=', 1);
})->where(function ($query) {
    $query->where('c', '=', 1)
          ->orWhere('d', '=', 1);
});

If you want to use parameters for a,b,c,d in Laravel 4

Model::where(function ($query) use ($a,$b) {
    $query->where('a', '=', $a)
          ->orWhere('b', '=', $b);
})
->where(function ($query) use ($c,$d) {
    $query->where('c', '=', $c)
          ->orWhere('d', '=', $d);
});

if you want to use parentheses in laravel 4 and don't forget return
In Laravel 4 (at least) you need to use $a, $b in parentheses as in the example

$a = 1;
$b = 1;
$c = 1;
$d = 1;
Model::where(function ($query) use ($a, $b) {
    return $query->where('a', '=', $a)
          ->orWhere('b', '=', $b);
})->where(function ($query) use ($c, $d) {
    return $query->where('c', '=', $c)
          ->orWhere('d', '=', $d);
});

This is my result: