I'd do this in this way (I put an own example for the loop):
{% for i in 0..9 %}
{% if loop.index0 % 2 == 0 %}
<div class="col-md-6"><!--start block-->
<div class="item-small gutter-bottom">
<img src="{{ item.image_url }}"/>
<div class="item-title">{{ item.name }}</div>
</div>
{% else %}
<div class="item-small gutter-bottom">
<img src="{{ item.image_url }}"/>
<div class="course-title">{{ item.name }}</div>
</div>
</div><!--end block-->
{% endif %}
{% endfor %}
You need to take care about the indexes of the loop, because if the 'if' code is not rendered first, your rendered html wouldn't be good, and the same occurs if in the last iteration the 'else' code is not rendered.