Intro to Hydrocarbons - Video Tutorials & Practice Problems
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concept
Intro To Hydrocarbons
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Now what carbon hydrocarbons are the simplest organic compounds composed solely of carbons and hydrogens. Here in this list we're going to go over different types of hydrocarbons. So, if we start with the first row, we have alkanes. Alcanes are just carbons that are single bonded to one another. Now if we pay attention, remember, each one of these bonds connects 2 carbons together, carbon must make 4 bonds. If we look at the 2 carbons in the middle, they each have 2 hydrogens. Now, focus on either one of these carbons, and you would see that they are connected to 4 surrounding atoms, meaning that their hybridization is s p 3. Their generic formula, if we were to look here, we'd have 4 carbons, and you would have 10 hydrogens. And that's because generic formula for an alkane is, CnH2n+2, where n is the number of carbon atoms. So if we said that we need an alkane that has 5 carbons, what is its molecular formula? It'd be C 5 H 2, times 5 plus 2, so that'd be C5 H12. Now, alkene's is when you have 2 carbons double bonded to each other, they still need to make 4 bonds, they're making 3 so they each have 1 hydrogen that's invisible. Notice that the number of hydrogens decreased as we added that Pi bond between the carbons. These carbons here are connected to 1, 2, 3 surrounding atoms, so they are SP 2 in terms of hybridization. Each of these double bonded carbons lost a Hydrogen, so we lost 2 Hydrogens overall. So our generic formula has changed to CnH2 2 N. We've dropped the plus 2 because we lost those 2 hydrogens. Alkyne are triple bonded carbons, so there's one here and here. They're making 4 bonds right now, so they don't need any extra hydrogens on them. These 2 s p s carbons are sp hybridized because they are connected to 2 surrounding atoms. And think about it, we just lost another 2 hydrogens, so the generic formula becomes CnH2N-two. Cycloalkanes are just alkanes that are in rings. So they're all still single bonded. In this ring, we have carbons all around. Each of these carbons has 2 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 1, 2, 3, 4 surrounding atoms, so it is SP 3 hybridized. Here if we look, we have 5 carbons for 10 hydrogens, so the ratio is there's double the amount of hydrogens to carbon. So that means the formula will be CnH2n. So a Cycloalkane has the same generic formula as an alkene. We have to lose 2 hydrogens in order to enclose this alkane into a ring. Finally, aromatic. Aromatic is really referring to a Benzene ring. A Benzene ring is 6 carbons in a ring with alternating double bonds. Each of these carbons has 1 hydrogen. So a Benzene has a formula of C6H6. 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 3 surrounding atoms, so they are sp2 hybridized. And here it's a one to one relationship between Carbon and Hydrogen since it's C6H6. So the generic formula is CNHN. Alright. So these encompass all the different types of hydrocarbons that you may encounter when deep 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 are in rings. Okay. But they're all hydrocarbons at the end of the day.
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example
Intro To Hydrocarbons Example
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So in this example question it says, classify each of the following hydrocarbons as an alkane, alkene, or alkyne. 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 2 carbons to each other. In this option B, all of them are single bonded to one another, so they're all alkanes. Well, it is an alkane. This is the only alkane that we have. An alkene is when we have carbons double bonded to one another. These 2 carbons here are double bonded to each other, and as long as 2 carbons are double bonded to each other, it is an alkene. These 2 carbons are double bonded to each other, so this is also an alkene. An alkyne is when we have 2 carbons triple bonded to one another. We have a carbon here, and a carbon here. So option C would represent an alkyne. So this is how we describe our options A, B, C, and D for the following example question.
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concept
Saturated and Unsaturated Hydrocarbons
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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 3 carbons have to make 4 bonds, and to do this we'd have to add hydrogens to them. An unsaturated would mean that we have at at least 1 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 max number of 3 hydrogens. But because of that double bond there, carbon again remember needs to make 4 bonds. This carbon here is already making 1, 2, 3 bonds, so it only needs 1 hydrogen. This carbon here is making 1, 2, 3 bonds, so it also needs 1 hydrogen here, and 1 hydrogen here. What's the difference? Well, these 2 carbons, this one here had 2 hydrogens, but with the inclusion of a double bond now it only has 1. This carbon here has 3 Hydrogens, but the inclusion of the double bond means now it has only 2. So adding a Pi bond, adding a double bond, means that we're gonna have to forfeit 1 hydrogen atom per carbon. And if we were to make a triple bond, again we'd have to forfeit 1 hydrogen atom between those carbons. Okay. So this is the difference between saturated where there are no double bonds or triple bonds, so you have the maximum 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
Intro To Hydrocarbons Example
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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 2. 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 4 bonds. Adding those Pi bonds decreases that number. Alright. 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
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concept
Bond Rotation and Spatial Orientation
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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 and 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 H would rotate to where this methyl group is, and then this, this CH3 group here would rotate up here. Now, if we have a double bond which is in alkenes, we cannot rotate. There's no free rotation around a pi bond, a double bond. This leads to 2 different spatial orientations and therefore 2 different compounds. These 2 carbons are double bonded so we can't rotate. That means that these 2 blues are locked on the same side and these 2 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 2 H's are locked on the same side, but here they're on opposite sides. There's no free rotation, so these will represent 2 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.
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example
Intro To Hydrocarbons Example
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Here it says determine if the two structures below are the same or different compounds. Well both compounds have 2 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 2 H's 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?