13. Which of the following Newman projections represents the most stable conformation of (S)-2,3-dimethylpentane? (A) H. H H. HCHC (A) (A) m/z 15 (C) m/z 57 CHCH3 CH CH CH OH CH3 CH3 H CH3 (B) 14. What is the base peak in the electron-impact mass spectrum of 3-pentanone? (D) (B) m/2 68 (D) m/2 71 1.03 2. (CH3)S H HCHC OH H HC H. (B) CHCH CH3 15. What is the major product of the following sequence? H CH H CH CH3 CH KCrO7 HSO4 OH OH