Wordpress Posts odd/even Li layout - php

Question

I am working on a custom theme and on one of the pages i need to style the posts pages as follows: http://gyazo.com/e1f7cfc03c7ba3981188077afcdf0314
The grey box is an image and the red box is content. I need to use perhaps an odd/even Li/Ul pseudo class/selector but i have no idea how to do it.
Could anyone offer me a way to start it up? I was thinking of using the Odd/Even pseudo class on UL to change the divs names however i can't think how to do it or where to start.
Thanks!
Edit: I am thinking perhaps odd/even selector combined with jquery prepend/append?
Edit2: this is what i have however it is displaying all the Odds first then all of the Evens instead of alternatively.
PHP:
<?php $i++; if(($i % 2) == 0) : $wp_query->next_post(); else : the_post(); ?>
<div class="section group">
<div class="col span_1_of_2 blue doubleheight">
<?php the_post_thumbnail('large'); ?>
</div>
<div class="col span_1_of_3_30 blue doubleheight">
<h2><?php the_title(); ?></h2>
<div class="post-text"><?php the_excerpt(); ?></div>
</div>
</div>
<?php echo $i; ?>
<?php endif; endwhile; ?>
<?php while(have_posts()) : ?>
<?php $i++; if(($i % 2) !== 0) : $wp_query->next_post(); else : the_post(); ?>
<div class="section group">
<div class="col span_1_of_3_30 blue doubleheight">
<h2><?php the_title(); ?></h2>
<div class="post-text"><?php the_excerpt(); ?></div></div>
<div class="col span_1_of_2 blue doubleheight">
<?php the_post_thumbnail('large'); ?>
</div>
</div>
<?php echo $i; ?>
<?php endif; endwhile; ?>

Answer 1

Since you are in the loop, you can use the build in loop counter ($wp_query->current-post) to add a different class to all odds or all evens or both
There is no need to run two loops. Here is an example of how I use this in my website to create two post columns
<?php if ( have_posts() ) : ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php /* Start the Loop */ ?>
<div class="entry-content-<?php if( $wp_query->current_post%2 == 1 ){ echo ' left-post';}else{ echo ' right-post';} ?>">
<?php get_template_part( 'content', get_post_format() ); ?>
</div>
<?php endwhile; ?>
EDIT
I misunderstood you in my original answer, but you can still use the same idea as I used there. Here is something you can try. Just replace all your code with this
<?php if ( have_posts() ) : ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php /* Start the Loop */
if($wp_query->current_post%2 == 1 ) { ?>
<div class="section group">
<div class="col span_1_of_2 blue doubleheight">
<?php the_post_thumbnail('large'); ?>
</div>
<div class="col span_1_of_3_30 blue doubleheight">
<h2><?php the_title(); ?></h2>
<div class="post-text">
<?php the_excerpt(); ?>
</div>
</div>
</div>
<?php }else{ ?>
<div class="section group">
<div class="col span_1_of_3_30 blue doubleheight">
<h2><?php the_title(); ?></h2>
<div class="post-text">
<?php the_excerpt(); ?>
</div>
</div>
<div class="col span_1_of_2 blue doubleheight">
<?php the_post_thumbnail('large'); ?>
</div>
</div>
<?php }
<?php endwhile; ?>
<?php endif; ?>