Who said they do? For pentane, for example, the trend is
n-pentane mp - 129.7
iso-pentane mp -159.9
tert-pentane mp -16.6
The
The unbranched pentane has only the second lowest mp, while the branched chain is lowest and the spherical one has the highest mp. The point at which a crystal melts is governed by the energy required to disrupt it, and while branching has a role in this, packing efficiency has a role also.
Who said they do? For pentane, for example, the trend is
n-pentane mp - 129.7
iso-pentane mp -159.9
tert-pentane mp -16.6
The
The unbranched pentane has only the second lowest mp, while the branched chain is lowest and the spherical one has the highest mp. The point at which a crystal melts is governed by the energy required to disrupt it, and while branching has a role in this, packing efficiency has a role also.
Longer carbon chains have stronger London dispersion forces. They pull the molecules together increasing the energy required to pull them apart and melt them.
Longer carbon chains have stronger London dispersion forces. They pull the molecules together increasing the energy required to pull them apart and melt them.
There isn't up and down the group.. Alkane is not a group in periodic table or anything.. but the melting point is directly proportional to the molecular mass of an alkane.. the longer the carbon chain, the higher the melting point
There isn't up and down the group.. Alkane is not a group in periodic table or anything.. but the melting point is directly proportional to the molecular mass of an alkane.. the longer the carbon chain, the higher the melting point
Boiling of compounds involve the breakage of bonds, greater the number of bonds greater will be the boiling point.
On moving from lower to higher members among the alkanes like methane, ethane , propane, butane and so on, there are increase in molecular mass and number of bonding which contribute to the increased boiling point.
Boiling of compounds involve the breakage of bonds, greater the number of bonds greater will be the boiling point.
On moving from lower to higher members among the alkanes like methane, ethane , propane, butane and so on, there are increase in molecular mass and number of bonding which contribute to the increased boiling point.
To expand Shivani’s answer, above, a little bit, the zig-zag chains of straight- chain Alkanes are able to fit snugly together, thus maximising the surface area in contact, and increasing the associative van Der Waals forces. Branches on the chain force the zig-zag chains apart, thus reducing the van der Waals forces.
To expand Shivani’s answer, above, a little bit, the zig-zag chains of straight- chain Alkanes are able to fit snugly together, thus maximising the surface area in contact, and increasing the associative van Der Waals forces. Branches on the chain force the zig-zag chains apart, thus reducing the van der Waals forces.
Why does the melting point of branched alkanes increase?
It doesn’t, according to data I found. At least not always. Here are melting points as I found them.
C4 alkanes
butane, -138º
isobutane, -160º
C5 alkanes
pentane, -130º
isopentane, -160º
neopentane, -17º
C6 alkanes
hexane, -95º
isohexane, -160º
3-methylhexane, -163º
2,3-dimethylbutane, -124º
neohexane, -98º
C7 alkanes
heptane, -90º
isoheptane, -119º
3-methylheptane, -119º
neoheptane, -124º
What I found was that the melting points of isomeric alkanes decreases with branching. This makes sense, because — unlike boiling point — melting point does not depend only on surface area. It also depends on “stackability” of the molecules in the solid.
Butane molecules stack on each other much better than isobutane molecules; the same is true for pentane vs. isopentane, hexane vs. isohexane, and heptane vs. isoheptane. (“Iso” means that the end carbon is removed and reattached two carbons in, to create a branch.)
The major anomalies are neopentane and neohexane, which are spherical or nearly so. Spheres stack very well, and so their melting points are higher than other branched isomers — or, in the case of neopentane, even the straight-chain isomer.
However, this is not true of neoheptane (2,2-dimethylpentane), as the 3-carbon-long “tail” interferes with the smooth sphericity of the molecule and results in poor stacking; you end up with a melting point comparable to the other branched C7 isomers.
Why does the melting point of branched alkanes increase?
It doesn’t, according to data I found. At least not always. Here are melting points as I found them.
C4 alkanes
butane, -138º
isobutane, -160º
C5 alkanes
pentane, -130º
isopentane, -160º
neopentane, -17º
C6 alkanes
hexane, -95º
isohexane, -160º
3-methylhexane, -163º
2,3-dimethylbutane, -124º
neohexane, -98º
C7 alkanes
heptane, -90º
isoheptane, -119º
3-methylheptane, -119º
neoheptane, -124º
What I found was that the melting points of isomeric alkanes decreases with branching. This makes sense, because — unlike boiling point — melting point does not depend only on surface area. It also depends on “stackability” of the molecules in the solid.
Butane molecules stack on each other much better than isobutane molecules; the same is true for pentane vs. isopentane, hexane vs. isohexane, and heptane vs. isoheptane. (“Iso” means that the end carbon is removed and reattached two carbons in, to create a branch.)
The major anomalies are neopentane and neohexane, which are spherical or nearly so. Spheres stack very well, and so their melting points are higher than other branched isomers — or, in the case of neopentane, even the straight-chain isomer.
However, this is not true of neoheptane (2,2-dimethylpentane), as the 3-carbon-long “tail” interferes with the smooth sphericity of the molecule and results in poor stacking; you end up with a melting point comparable to the other branched C7 isomers.
Well, they have longer hydrocarbyl chains …. and the LONGER the chain, the MORE opportunity the molecule has for chain-chain interaction. And so let us review the data…
Well, they have longer hydrocarbyl chains …. and the LONGER the chain, the MORE opportunity the molecule has for chain-chain interaction. And so let us review the data…
Neither one. As an unanimated entity salt is devoid of actions and cannot increase its melting point.
Neither one. As an unanimated entity salt is devoid of actions and cannot increase its melting point.
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Who said they do? For pentane, for example, the trend is
n-pentane mp - 129.7
iso-pentane mp -159.9
tert-pentane mp -16.6
The
The unbranched pentane has only the second lowest mp, while the branched chain is lowest and the spherical one has the highest mp. The point at which a crystal melts is governed by the energy required to disrupt it, and while branching has a role in this, packing efficiency has a role also.
Who said they do? For pentane, for example, the trend is
n-pentane mp - 129.7
iso-pentane mp -159.9
tert-pentane mp -16.6
The
The unbranched pentane has only the second lowest mp, while the branched chain is lowest and the spherical one has the highest mp. The point at which a crystal melts is governed by the energy required to disrupt it, and while branching has a role in this, packing efficiency has a role also.
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Longer carbon chains have stronger London dispersion forces. They pull the molecules together increasing the energy required to pull them apart and melt them.
Longer carbon chains have stronger London dispersion forces. They pull the molecules together increasing the energy required to pull them apart and melt them.
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There isn't up and down the group.. Alkane is not a group in periodic table or anything.. but the melting point is directly proportional to the molecular mass of an alkane.. the longer the carbon chain, the higher the melting point
There isn't up and down the group.. Alkane is not a group in periodic table or anything.. but the melting point is directly proportional to the molecular mass of an alkane.. the longer the carbon chain, the higher the melting point
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I will suggest that increasing the length of the alkane chain makes the molecule more hydrophobic and less able to be conductive.
I will suggest that increasing the length of the alkane chain makes the molecule more hydrophobic and less able to be conductive.
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Boiling of compounds involve the breakage of bonds, greater the number of bonds greater will be the boiling point.
On moving from lower to higher members among the alkanes like methane, ethane , propane, butane and so on, there are increase in molecular mass and number of bonding which contribute to the increased boiling point.
Boiling of compounds involve the breakage of bonds, greater the number of bonds greater will be the boiling point.
On moving from lower to higher members among the alkanes like methane, ethane , propane, butane and so on, there are increase in molecular mass and number of bonding which contribute to the increased boiling point.
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To expand Shivani’s answer, above, a little bit, the zig-zag chains of straight- chain Alkanes are able to fit snugly together, thus maximising the surface area in contact, and increasing the associative van Der Waals forces. Branches on the chain force the zig-zag chains apart, thus reducing the van der Waals forces.
To expand Shivani’s answer, above, a little bit, the zig-zag chains of straight- chain Alkanes are able to fit snugly together, thus maximising the surface area in contact, and increasing the associative van Der Waals forces. Branches on the chain force the zig-zag chains apart, thus reducing the van der Waals forces.
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Why does the melting point of branched alkanes increase?
It doesn’t, according to data I found. At least not always. Here are melting points as I found them.
C4 alkanes
C5 alkanes
C6 alkanes
C7 alkanes
What I found was that the melting points of isomeric alkanes decreases with branching. This makes sense, because — unlike boiling point — melting point does not depend only on surface area. It also depends on “stackability” of the molecules in the solid.
Butane molecules stack on each other much better than isobutane molecules; the same is true for pentane vs. isopentane, hexane vs. isohexane, and heptane vs. isoheptane. (“Iso” means that the end carbon is removed and reattached two carbons in, to create a branch.)
The major anomalies are neopentane and neohexane, which are spherical or nearly so. Spheres stack very well, and so their melting points are higher than other branched isomers — or, in the case of neopentane, even the straight-chain isomer.
However, this is not true of neoheptane (2,2-dimethylpentane), as the 3-carbon-long “tail” interferes with the smooth sphericity of the molecule and results in poor stacking; you end up with a melting point comparable to the other branched C7 isomers.
Why does the melting point of branched alkanes increase?
It doesn’t, according to data I found. At least not always. Here are melting points as I found them.
C4 alkanes
C5 alkanes
C6 alkanes
C7 alkanes
What I found was that the melting points of isomeric alkanes decreases with branching. This makes sense, because — unlike boiling point — melting point does not depend only on surface area. It also depends on “stackability” of the molecules in the solid.
Butane molecules stack on each other much better than isobutane molecules; the same is true for pentane vs. isopentane, hexane vs. isohexane, and heptane vs. isoheptane. (“Iso” means that the end carbon is removed and reattached two carbons in, to create a branch.)
The major anomalies are neopentane and neohexane, which are spherical or nearly so. Spheres stack very well, and so their melting points are higher than other branched isomers — or, in the case of neopentane, even the straight-chain isomer.
However, this is not true of neoheptane (2,2-dimethylpentane), as the 3-carbon-long “tail” interferes with the smooth sphericity of the molecule and results in poor stacking; you end up with a melting point comparable to the other branched C7 isomers.
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Well, they have longer hydrocarbyl chains …. and the LONGER the chain, the MORE opportunity the molecule has for chain-chain interaction. And so let us review the data…
Well, they have longer hydrocarbyl chains …. and the LONGER the chain, the MORE opportunity the molecule has for chain-chain interaction. And so let us review the data…
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