Question

How does this Gas Chromatography graph support Saytzeffs rule?

(Our lab was dehydration of 2-methylcyclohexanol)

Chrom Perfect Chromatogram Report Sample Name Acquisition Port - OP Instrument Instrument 2 Heading 1 Heading 2 Raw File Name - CACPSpiralkanes(1).0019.RAW Method File Name - CCPSpirita anemic met Method Description Calibration File Name Internal External (No data Date Taken (end) - 10/29/2009 12:37:03 PM Method Version20 Method Dale - 10/28/2009 5 10 35 PM Calibration Version0 Calibration Date - No datal Run Time - 4.465841 Amount injected Sample Weight 1 Data Sampling Rate - 5.131546 Dution Factor 1 Int Sud Amount=1 Peak With = 0.05 Peak Threshold Operator Manual integration no manually Integrated Peak Rot Time Name Amount 0.00 Area 16905 Area 24297 Type EV Width 023 75.703 Total Area -60573.13 Total Height=4136.321 Total Amount = 0 CWTON 10/21/07 5 uk dample Col:150%; DET: 1600. INT: 140°C; Printed on 10729 2009 1237 07 PM PORT "B" Row= 45 ml/min Polariry "" Page 1 od 1

Answer 1

According to Saytzeff rule, the major dehydration product will be 1-methylcyclohexene (poor becomes poorer which means hydrogen will be eliminated from the neighboring carbon containing less number of hydrogen atoms). In the Gas Chromatography (GC) the major product (higher peak) has higher retention time, RT (comes out of the GC column later), which means it's boiling point (BP) is higher. We know, the BP of 1-methylcyclohexene (~ 110 C) is higher than that of 3-methylcyclohexene (~ 104 C). Therefore, the GC graph supports Saytzeff rule as the major dehydration product 1-methylcyclohexene (higher peak) has higher RT due to its higher BP.

OH Dehydration (-120) 2-methyleyebhexand 1- mithylcyclohexene ( Saytzeff product) Higher be 3- methyl eyelohexene ( Hofmann product) Lower BP