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What is the structural formula of the following compounds, octane C8H18?
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Little Yellowbird
What is the structural formula of the following compounds, octane C8H18?
Well, you gots a saturated alkane here, i.e. whose formula corresponds to [math]C_{n}H_{2n+2}[/math], i.e. [math]n=8[/math]. And octane generates some 18 structural isomers … some of which can further generate optical isomerism.
[math] ext{2,2,4-Trimethylpentane}[/math], i.e. [math] ext{isooctane}[/math] was chosen as the standard for the octane rating in the internal combustion engine….
Well, you gots a saturated alkane here, i.e. whose formula corresponds to [math]C_{n}H_{2n+2}[/math], i.e. [math]n=8[/math]. And octane generates some 18 structural isomers … some of which can further generate optical isomerism.
[math]ext{2,2,4-Trimethylpentane}[/math], i.e. [math]ext{isooctane}[/math] was chosen as the standard for the octane rating in the internal combustion engine….
There are 18 different physical shapes (isomers) of C8H18 - octane, and they all have different physical and chemical properties. Those physical shapes have the hydrogen and carbon atoms in different groups and positions.
For example, n-octane has the eight carbon atoms arranged in a row (straight chain) with the eighteen hydrogen atoms arranged around that chain evenly. But you can also take a methyl group (CH3) out of that chain and place it off to the side of say the second carbon atom. Now you have seven carbon in a row and one carbon with three hydrogen sticking out to one side - 2 methyl heptane (second carbon atom of seven having a methyl CH3 group to the side). It's still C8H18 but the atoms are just arranged differently. That's possible to do eighteen different ways with C8H18 - octane
One of those isomers, 2,2,4 trimethyl pentane (iso octane) has a particular property which is useful in gasoline engines - it's very stable during combustion and so it resists detonation (uncontrolled combustion) during the combustion event, and was chosen by Graham Edgar (Ethyl Corp) in 1927, as the 100 point for his proposed octane rating system for comparing with various gasoline mixtures.
Normal octane, n-octane (still C8H18) has a terrible resistance to detonation, actually MINUS 18, but it was deliberately NOT chosen as the zero point for the octane rating as it has quite different physical properties to iso-octane, different density, different evaporation rate, different boiling point (126c) and so on.
Edgar was well aware that there were other compounds like Toluene C7H8, and Bensene/Benzol C6H6 which had higher detonation resistance than iso-octane, but he needed compounds with similar physical properties, and he could not find low detonation resistant compounds physically close enough to make a "wider" scale with those high detonation resistant compounds.
Instead, Edgar chose n-heptane as the zero point. It too has a low detonation resistance, but in its physical properties it's similar to iso-octane, and in particular, it has almost the same boiling point of 98c, so various mixtures of the two compounds won't skew the results when testing those mixtures against other forms of gasoline to determine the octane rating of those gasolines.
The other reason for choosing iso-octane and n-heptane is that both could be obtained/extracted in pure form (1927 renember) relatively easily. That's important when you think that gallons of them would be used in the test engines, not millilitres.
So now we have gasoline with various octane ratings including higher than 100, since adding things like Toluene, xylene, or ethanol take the detonation resistance past that of iso-octane, and we have other compounds with detonation ratings less than zero because they detonate more easily than n-heptane.
There are 18 different physical shapes (isomers) of C8H18 - octane, and they all have different physical and chemical properties. Those physical shapes have the hydrogen and carbon atoms in different groups and positions.
For example, n-octane has the eight carbon atoms arranged in a row (straight chain) with the eighteen hydrogen atoms arranged around that chain evenly. But you can also take a methyl group (CH3) out of that chain and place it off to the side of say the second carbon atom. Now you have seven carbon in a row and one carbon with three hydrogen sticking out to one side - 2 methyl heptane (second carbon atom of seven having a methyl CH3 group to the side). It's still C8H18 but the atoms are just arranged differently. That's possible to do eighteen different ways with C8H18 - octane
One of those isomers, 2,2,4 trimethyl pentane (iso octane) has a particular property which is useful in gasoline engines - it's very stable during combustion and so it resists detonation (uncontrolled combustion) during the combustion event, and was chosen by Graham Edgar (Ethyl Corp) in 1927, as the 100 point for his proposed octane rating system for comparing with various gasoline mixtures.
Normal octane, n-octane (still C8H18) has a terrible resistance to detonation, actually MINUS 18, but it was deliberately NOT chosen as the zero point for the octane rating as it has quite different physical properties to iso-octane, different density, different evaporation rate, different boiling point (126c) and so on.
Edgar was well aware that there were other compounds like Toluene C7H8, and Bensene/Benzol C6H6 which had higher detonation resistance than iso-octane, but he needed compounds with similar physical properties, and he could not find low detonation resistant compounds physically close enough to make a "wider" scale with those high detonation resistant compounds.
Instead, Edgar chose n-heptane as the zero point. It too has a low detonation resistance, but in its physical properties it's similar to iso-octane, and in particular, it has almost the same boiling point of 98c, so various mixtures of the two compounds won't skew the results when testing those mixtures against other forms of gasoline to determine the octane rating of those gasolines.
The other reason for choosing iso-octane and n-heptane is that both could be obtained/extracted in pure form (1927 renember) relatively easily. That's important when you think that gallons of them would be used in the test engines, not millilitres.
So now we have gasoline with various octane ratings including higher than 100, since adding things like Toluene, xylene, or ethanol take the detonation resistance past that of iso-octane, and we have other compounds with detonation ratings less than zero because they detonate more easily than n-heptane.
Well, you gots a saturated alkane here, i.e. whose formula corresponds to [math]C_{n}H_{2n+2}[/math], i.e. [math]n=8[/math]. And octane generates some 18 structural isomers … some of which can further generate optical isomerism.
[math] ext{2,2,4-Trimethylpentane}[/math], i.e. [math] ext{isooctane}[/math] was chosen as the standard for the octane rating in the internal combustion engine….
Well, you gots a saturated alkane here, i.e. whose formula corresponds to [math]C_{n}H_{2n+2}[/math], i.e. [math]n=8[/math]. And octane generates some 18 structural isomers … some of which can further generate optical isomerism.
[math]ext{2,2,4-Trimethylpentane}[/math], i.e. [math]ext{isooctane}[/math] was chosen as the standard for the octane rating in the internal combustion engine….
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There are 18 different physical shapes (isomers) of C8H18 - octane, and they all have different physical and chemical properties. Those physical shapes have the hydrogen and carbon atoms in different groups and positions.
For example, n-octane has the eight carbon atoms arranged in a row (straight chain) with the eighteen hydrogen atoms arranged around that chain evenly. But you can also take a methyl group (CH3) out of that chain and place it off to the side of say the second carbon atom. Now you have seven carbon in a row and one carbon with three hydrogen sticking out to one side - 2 methyl heptane (second carbon atom of seven having a methyl CH3 group to the side). It's still C8H18 but the atoms are just arranged differently. That's possible to do eighteen different ways with C8H18 - octane
One of those isomers, 2,2,4 trimethyl pentane (iso octane) has a particular property which is useful in gasoline engines - it's very stable during combustion and so it resists detonation (uncontrolled combustion) during the combustion event, and was chosen by Graham Edgar (Ethyl Corp) in 1927, as the 100 point for his proposed octane rating system for comparing with various gasoline mixtures.
Normal octane, n-octane (still C8H18) has a terrible resistance to detonation, actually MINUS 18, but it was deliberately NOT chosen as the zero point for the octane rating as it has quite different physical properties to iso-octane, different density, different evaporation rate, different boiling point (126c) and so on.
Edgar was well aware that there were other compounds like Toluene C7H8, and Bensene/Benzol C6H6 which had higher detonation resistance than iso-octane, but he needed compounds with similar physical properties, and he could not find low detonation resistant compounds physically close enough to make a "wider" scale with those high detonation resistant compounds.
Instead, Edgar chose n-heptane as the zero point. It too has a low detonation resistance, but in its physical properties it's similar to iso-octane, and in particular, it has almost the same boiling point of 98c, so various mixtures of the two compounds won't skew the results when testing those mixtures against other forms of gasoline to determine the octane rating of those gasolines.
The other reason for choosing iso-octane and n-heptane is that both could be obtained/extracted in pure form (1927 renember) relatively easily. That's important when you think that gallons of them would be used in the test engines, not millilitres.
So now we have gasoline with various octane ratings including higher than 100, since adding things like Toluene, xylene, or ethanol take the detonation resistance past that of iso-octane, and we have other compounds with detonation ratings less than zero because they detonate more easily than n-heptane.
There are 18 different physical shapes (isomers) of C8H18 - octane, and they all have different physical and chemical properties. Those physical shapes have the hydrogen and carbon atoms in different groups and positions.
For example, n-octane has the eight carbon atoms arranged in a row (straight chain) with the eighteen hydrogen atoms arranged around that chain evenly. But you can also take a methyl group (CH3) out of that chain and place it off to the side of say the second carbon atom. Now you have seven carbon in a row and one carbon with three hydrogen sticking out to one side - 2 methyl heptane (second carbon atom of seven having a methyl CH3 group to the side). It's still C8H18 but the atoms are just arranged differently. That's possible to do eighteen different ways with C8H18 - octane
One of those isomers, 2,2,4 trimethyl pentane (iso octane) has a particular property which is useful in gasoline engines - it's very stable during combustion and so it resists detonation (uncontrolled combustion) during the combustion event, and was chosen by Graham Edgar (Ethyl Corp) in 1927, as the 100 point for his proposed octane rating system for comparing with various gasoline mixtures.
Normal octane, n-octane (still C8H18) has a terrible resistance to detonation, actually MINUS 18, but it was deliberately NOT chosen as the zero point for the octane rating as it has quite different physical properties to iso-octane, different density, different evaporation rate, different boiling point (126c) and so on.
Edgar was well aware that there were other compounds like Toluene C7H8, and Bensene/Benzol C6H6 which had higher detonation resistance than iso-octane, but he needed compounds with similar physical properties, and he could not find low detonation resistant compounds physically close enough to make a "wider" scale with those high detonation resistant compounds.
Instead, Edgar chose n-heptane as the zero point. It too has a low detonation resistance, but in its physical properties it's similar to iso-octane, and in particular, it has almost the same boiling point of 98c, so various mixtures of the two compounds won't skew the results when testing those mixtures against other forms of gasoline to determine the octane rating of those gasolines.
The other reason for choosing iso-octane and n-heptane is that both could be obtained/extracted in pure form (1927 renember) relatively easily. That's important when you think that gallons of them would be used in the test engines, not millilitres.
So now we have gasoline with various octane ratings including higher than 100, since adding things like Toluene, xylene, or ethanol take the detonation resistance past that of iso-octane, and we have other compounds with detonation ratings less than zero because they detonate more easily than n-heptane.
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