Classify the carbon atoms of $CH X_{3} - CH X_{2} - C (CH X_{3}) X_{2} - CH (CH X_{3}) - CH X_{2} - CH (CH X_{3}) - CH X_{2} - CH X_{3}$ (a quaternary carbon is bonded to four carbons). How many primary, secondary, tertiary and quaternary carbons, respectively, does it contain?

A7, 2, 2, 1
B6, 3, 3, 0
C6, 3, 2, 1
D5, 4, 2, 1

Answer: C

Count the carbon neighbours of each of the 12 carbons. The CH3 groups (C1 of the chain, the two methyls on C3, the methyl on C4, the methyl on C6 and the terminal CH3) are 6 primary carbons. The CH2 carbons are 3 secondary carbons. The CH carbons (C4 and C6) are 2 tertiary carbons. C3 is the single quaternary carbon. The total is 6+3+2+1 = 12.

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Classify the carbon atoms of CHX3​−CHX2​−C(CHX3​)X2​−CH(CHX3​)−CHX2​−CH(CHX3​)−CHX2​−CHX3​ (a quaternary carbon is bonded to four carbons). How many primary, secondary, tertiary and quaternary carbons, respectively, does it contain?

Answer: C

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Classify the carbon atoms of $CH X_{3} - CH X_{2} - C (CH X_{3}) X_{2} - CH (CH X_{3}) - CH X_{2} - CH (CH X_{3}) - CH X_{2} - CH X_{3}$ (a quaternary carbon is bonded to four carbons). How many primary, secondary, tertiary and quaternary carbons, respectively, does it contain?