When Germany invaded russia they went straight to stalingrad, They had a option to go south to caucasus but hitler Chose not to because he Wanted to take Stalingrad and erase its name, If they decided to go down to caucasus which had oil refineries
It would have increased their chances of winning, They hoped to getting to stalingrad before the winter but they failed, The russians are well prepared for winter warfare while the germans were not prepared at all, This pushed back germany.