Question

Propose three reasonable molecular formulas for a molecular ion at m/z = 176, (show calculations; 3 pts) Propose two reasonable structures for a hydrocarbon having an exact mass of 122.1096 that forms 1-ethyl-1-methylcyclohexane upon hydrogenation with excess H2 and Pd-C. (2 pts) 3. 4. A low resolution mass spectrum of a neurotransmitter gave a molecular ion at m/z s 153. Three possible formulas for this molecular ion are Coth/N,O2. Cat,NO, and C,HnN,O. A high resolution mass spectrum provided a exact mass of 153,0790. Circle the correct molecular formula. (1.5 pts) 5. Calculate the number of degrees of unsaturation for C,HeN,O. (show calculations; 1.5 pts)

Answer 1

2) applying rule 13 for hydrocarbon

General formula for hydrocarbon = C_nH_n+r

n= number of carbon atom

r = remainder

Step1: devide the molecular weight by 13.

176/13= 13.5385  

That is number of carbon atom (n) = 13

Step2: multiply the remainder by 13.

13 × 0.5385 = 7.0005~ 7

Therefore number of hydrocarbon = n + r = 13+ 7 =20

Step3 : hydrocarbon formula

C₁₃H₂₀

Step4 : since molecular weight and number of hydrogen atom is even. Threfore there is possibility of oxygen atom.

For each oxygen atom replace CH4.

Hence molecular formulas containing oxygen atom are given as

C₁₂H₁₆O , C₁₁H₁₂O₂

Hence three reasonable molecular formulas

C₁₃H₂₀ , C₁₂H₁₆O , C₁₁H₁₂O_2.