Intro to Hydrocarbons - Video Tutorials & Practice Problems
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Intro to Hydrocarbons Concept 1
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Now we call the hydrocarbons are the simplest organic compounds composed solely of carbons and hydrogens. Here in this list, we're gonna go over different types of hydrocarbons. So if we start with the first draw, we have alkanes, alkanes are just carbons that are single bonded to one another. Now, if we pay attention, remember each one of these bonds connects two carbons together, carbon must make four bonds. If we look at the two carbons in the middle, they each have two hydrogens. Now focus on either one of these carbons and you would see that they are connected to four surrounding atoms, meaning that their hybridization is sp three, their generic formula. If we were to look here, we'd have four carbons and you would have 10 hydrogens. And that's because generic formula for an alkane is CNH two N plus two or N is the number of carbon atoms. So if we said that we need an alkane that has five carbons, what is its molecular formula? It'd be C five H two times five plus two. So that'd be C five H 12. Now, Keynes is when you have two carbons double bonded to each other, they still need to make four bonds, they're making three. So they each have one hydrogen that's invisible. Notice that the number of hydrogens decreased as we added, that pi bond between the carbons, these carbon sea are connected to 123 surrounding atoms. So they are sp two in terms of hybridization, each of these double bodied carbons lost a hydrogen. So we lost two hydrogens overall. So our generic formula has changed to CNH two N. We've dropped the plus two because we've lost those two hydrogens. All kinds are triple bonded carbons. So there's one here and here they're making four bonds right now. So they don't need any extra hydrogens on them. These two SPS carbons are sp hybridized because they are connected to two surrounding atoms and think about it, we just lost another two hydrogen. So the generic formula becomes CNH two N minus two CYO Alkanes are just al canes that are in rings if we, so they're all still single bodied in this ring. We have carbons all around each of these carbons has two hydrogens on them, right? So if we think about it, focus on one of them, let's focus on this one right here. It is connected to 1234 surrounding atoms. So it is sp three hybridized here. If we looked, we have five carbons for 10 hydrogen. So the ratio is there's double the amount of hydrogen to carbon. So that means the formula will be CNH two N. So a cycle alkane has the same generic formula as an alkene. We had to lose two hydrogens in order to enclose this alkane into a rink. Finally, aromatic aromatic is really referring to a benzene ring. A benzene ring is six carbons in a ring with alternating double bonds, each of these carbons has one hydrogen. So benzene has a formula of C six H six. Another way of showing it is like this, this is changing it into more of a skeletal formula. Each of those carbons are double bonded, they're each connected to three surrounding atoms. So they are sp two hybridized. And here it's a 1 to 1 relationship between carbon and hydrogen since it's C six H six. So the generic formula is CNHN, right? So these encompass all the different types of hydrocarbons that you may encounter when de dealing with deeper types of ideas in organic chemistry. But remember essentially they're all just compounds with carbons and hydrogens. Here, some of them have single bonds, some of them have double bonds, some of them have triple bonds or or in rings. OK. But they're all hydrocarbons at the end of the day.
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example
Intro to Hydrocarbons Example 1
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So in this example, question, it says classify each of the following hydrocarbons as an alkane alkene or alky. So remember an alkane is when we have carbons just single bonded to one another. If we take a look at the options, remember every line connects two carbons to each other. In this option, B all of them are single bondt to one another. So they're all alkanes. Well, it is an alkane. This is the only Al king that we have and our keen is when we have carbons double bonded to one another. These two carbons here are double bonded to each other. And as long as two carbons are double bonded to each other, it is an alkene. These two carbons are double bonded to each other. So this is also an alkene and our kind is when we have two carbons triple bonded to one another, we have a carbon here and a carbon here. So option C would represent an alive. So this is how we describe our options, ABC and D. From the following example, question
3
concept
Saturated and Unsaturated Hydrocarbons Concept 2
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2m
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Now, with hydrocarbons, we now talk about saturated versus unsaturated. Now, a saturated hydrocarbon means that all the bonds are single bonds. So all the carbons connected to each other are single bonds. This allows each carbon to have a max possible number of hydrogen atoms. So if we take a look here at this image, the one on the left is a saturated hydrocarbon. Those three carbons have to make four bonds. And to do this, we'd have to add hydrogens to them. An unsaturated would mean that we have at l at least one double bond or triple bond, double or triple bond, meaning that we won't be able to have a maximum number of hydrogens. So if we take a look here, we have this double bond here, what effect will that have? Well, the carbon on the left is single bonded. So it still has its maximum number of three hydrogens. But because of that double bond there, carbon again, remember needs to make four bonds. This carbon here is already making 123 bonds. So it only needs one hydrogen. This carbon here is making 123 bonds. So it also needs one hydrogen here and one hydrogen here. What's the difference? Well, these two carbons, this one here had two hydrogens but with the inclusion of a double bond, not only has one, this carbon here has three hydrogens, but the inclusion of the double bond means now it has only two. So adding a pi bond, adding a double bond means that we're gonna have to forfeit one hydrogen atom per carbon. And if we were to make a triple bond again, we'd have to forfeit one hydrogen atom between those carbons. OK. So this is the difference between saturated where there are no double bonds or triple bonds. So you have the max number of hydrogen atoms on carbons and an unsaturated hydrocarbon where now double bonds and triple bonds decrease the total number of H atoms possible.
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example
Saturated and Unsaturated Hydrocarbons Example 2
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Here in this example, question, it says classify the following hydrocarbons as saturated or unsaturated. Remember, a saturated hydrocarbon possesses only single bonds between its carbons. In this image A and C would represent saturated hydrocarbons. Every line connects carbons together. All these carbons are single bonded to one another. Meaning they'll have a maximum number of hydrogen atoms attached to each of them unsaturated would be these two unsaturated hydrocarbons have a double bond or a triple bond present. This decreases the maximum number of H atoms that can connect to a potential carbon. Remember, carbon must make four bonds, adding those pi bonds decreases that number, right. So A and C would be saturated. B and D would be unsaturated.
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Problem
Problem
Write the molecular formula for an alkane with 5 C atoms.
A
C5H12
B
C5H10
C
C5H14
D
C5H8
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Problem
Problem
Write the molecular formula for an alkyne with 4 C atoms.
A
C4H8
B
C4H10
C
C4H6
D
C4H4
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Problem
Problem
Which of the following molecular formulas might indicate an alkene?
A
C7H16
B
C6H12
C
C5H8
D
C4H10
8
concept
Bond Rotation and Spatial Orientation Concept 3
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2m
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So in our continued discussion of hydrocarbons, we're now going to take a look at bond rotation and spatial orientation here, we're going to say carbon carbon bonds in alkanes can rotate freely. And that's because of the presence of a single bond. So here this is a carbon and this is a carbon and we rotate around this single bond. Now by rotating that we're gonna keep one side stationary, meaning we're not gonna move it, we're gonna keep this side still. So that matches up with this side and we're gonna rotate the other part, the right side when I'm rotating. So this red ball is up here. So when I rotate, it'll rotate down to where the blue is. So there it goes right there. And then when I rotate that down, this blue comes to where this part is. So there goes the blue part right there. And then that green thing has to shift up to this to where the red was. So there's the green part right up here. How would this look like in terms of a skeletal formula? So again, there's free rotation around the single bond. So we rotate, we keep this side stationary. So it stays where it is. Everything else is spinning. This oh would rotate to down to where the down to where the H is. So that's why it's here. This would rotate to where this methyl group is. And then this uh this ch three group here would rotate up here. Now, if we have a double bond, which is in our Keynes, we cannot rotate. There's no free rotation around a pi bond, a double bond. This leads to two different spatial orientations. And therefore two different compounds. These two carbons are double bonded. So we can't rotate. That means that these two blues are locked on the same side and these two greens are locked on the same side. So it would not be equal to the this molecule here where the blues are opposites of each other and the greens are on opposite sides of each other. If we show this as a skeletal formula, these two HS are locked on the same side, but here they're on opposite sides, there's no free rotation. So these will represent two different compounds. So just keep in mind when we're dealing with double bonds and also triple bonds, there's no free rotation around that bond. Things are locked where they are.
9
example
Bond Rotation and Spatial Orientation Example 3
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51s
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Here, it says, determine if the two structures below are the same or different compounds. Well, both compounds have two carbons double bonded to each other. Remember there is no free rotation around that double bond. So things are stuck where they are. The one on the left has an H and an F next to each other. But the one on the right has two ages instead next to each other. The one on the left has a BR and an H next to each other. But this one here has a BR and an F next to each other. We have different groups next to one another in both molecules or both compounds. And we can't rotate around that double bond so that they're the same because of this, they would represent different compounds. So here, our answer would be option B.
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Problem
Problem
Which of the following is not a valid bond rotation?
A
B
C
D
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