Side bar Random post PHP or condition

Hi guys,
My website layout is very complex with unique category templates and side bars. I am trying to have the same sidebar for single posts and chose categories but it is not working.

<?php if (is_single()) { <– works
<?php if (is_single() || is_category()) { <- works but i dont want it in all categories
<?php if (is_single(‘8’)) { <– doesn’t work, i made sure the category is 8 and i tried also the category name with no luck.

Thanks

<div class="sidebarbox">

     <!-- related posts sidebar -->
<?php if (is_single() || is_category('8')) {
	if (get_the_category()) {
?>

<?php
		foreach((get_the_category()) as $category) {
			echo '<h2>Related Posts: '.$category->cat_name.'</h2>'."\r\n<ul>";
			query_posts('cat='.$category->cat_ID.'&limit=10');
			while (have_posts()) {
				the_post();
?>
				<li><a href="<?php the_permalink() ?>" title="permalink to <?php the_title() ?>"><?php the_title() ?></a></li>
<?php
			}
			echo "</ul>\r\n";
		}
	}
}?>
         </div>