Complex sentence: Kerogens are chemical compounds that comprise the segment of organic matter in sedimentary rocks insoluble in the normal organic solvents because of its huge molecular weight (upwards of 1,000).
Split into simpler sentences: Kerogens are chemical compounds that make up a portion of the organic matter in sedimentary rocks. They are insoluble in normal organic solvents because of thier huge molecular weight (upwards of 1,000).