Notes for Week 4
Notes for Week 4 Chem 345
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This 3 page Class Notes was uploaded by Bethany Lawler on Friday September 18, 2015. The Class Notes belongs to Chem 345 at Washington State University taught by Dr. Crouch in Summer 2015. Since its upload, it has received 16 views. For similar materials see Organic Chemistry 1 in Chemistry at Washington State University.
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Date Created: 09/18/15
Chemistry 345 Week 4 9 14 9 18 Boiling points 0 The greater the attractive forces between molecules in a compound the higher the boiling point of the compound 0 The three types of attractive forces are 0 Van deer Waals Slight attractive forces created when the electrons create areas of high negative charge because of their random distribution Temporary and very small 0 Dipoledipole Attractive force between permanent dipoles of a molecule 0 Hydrogen bonding Attraction between the dipole of a molecule when one or more of their hydrogens are attached to an oxygen or nitrogen These are a form of dipole interactions but as so strong they are classified separately Alkanes 0 Larger chains of aliases have higher boiling points 0 Albanese only possess Van deer Waals attractive forces therefore the attraction is highly dependent on the surface area of the molecule The higher the surface area the better the attraction between the molecules 0 Chains that contain many carbons but have more branches and therefore less surface area for its mass have lower boiling points because the attractive forces aren t as strong Dipole interaction 0 The shape of the molecule effects that strength of the dipole Some molecules have stronger or weaker dipole than expected because of this Solubility 0 Like dissolves like Solvation 0 When in solution solvent particles surround the solute particles orienting their dipoles toward the oppositely charged poles of salute particles 0 Smaller nonpolar molecules are more likely to be soluble in a polar substance then large nonpolar molecules 0 The more nonpolar r groups a molecule contains and the larger they are the less likely they are to be soluble in polar solvents Confirmation states 0 Because sigma bonds can rotate the position of the r groups attached to the molecules in the bond can have different positions relative to one another 0 The different positions of the r groups cause the molecules to have different energies 0 The closer to each other the r groups are the higher the energy of that confirmation state 0 Newman projections o Newman projects are a way of drawing a sigma bond to evaluate the confirmation state 0 A Newman projection draws the two atoms along the sigma bond as though they were right on top of each other in other words as though the molecule was being seen along the line of the sigma bond being evaluated 0 The highest energy state is called an eclipsed state and in a Newman projection it appears as though the r groups are on top of each other 0 The lowest energy state is called the staggered state and in the Newman projection the r groups are equidistant from each other 0 When drawing a Newman projection there should only every be three r groups seen these can be very large though 7 Relative Energies The energies of all eclipsed states are the same when all r groups are the same and the energy of all the staggered states is the same when all r groups are the same If one atom has an one two or all three r groups different from the r groups on the other atom the staggered states all still have the same energy relative to one another and all the eclipsed states still have the same energy relative to one another If both atoms have one or more r groups different from the others the eclipsed and staggered states have different energies The highest energy is when the largest r groups are closest to each other and the lowest is when they are farthest away 8 Conformation States for Cyclic molecules The rings of cyclic molecules have a plane they are not always perfectly at but they are mostly at Substituents can therefore be either above or below the plane of the ring When a cyclic molecule has two substituents and they are both above or below the plane of the ring they are cis When one is above and one is below it is called trans When a cyclic molecule has cis and trans isomers then either cis or trans must be added to the front of the name 9 Cyclohexane confirmation states The lowest confirmation state of a cyclohexane with no substituents is called chair The chair con rmation has three of the carbons above the plane of the ring and three below They alternate around the ring The Substituents on the carbons can be classified as either axial up or down which means that they are roughly 90 to the plane of the ring or equatorial up or down meaning they are very close to the plane of the ring When substituents are added to the carbons that are not hydrogen they change the energy of the confirmations The lowest energy confirmation for a cyclohexane with one or more substituents is the conformation where the largest substituent is either equatorial up or equatorial down o The lowest energy state is the lowest because the axial substituents interact with each other whereas the equatorial don t 0 For cyclohexane that have two substituents there are cis and trans isomers o A cis isomer would have both substituents up or down regardless of whether they are axial or equatorial o A trans isomer would have one substituent up and one down regardless of whether they were axial or equatorial 0 Disubstituted cyclohexanes cyclohexanes with two substituents can also have the substituents in three orientations relative to each other 0 Directly across from each other across the ring two carbons between them 0 One carbon apart a single carbon between them 0 One neighboring carbons 10 Stereochemistry 0 The study of molecules that have isomers that are mirror images of each other 0 Isomers can be diVided into two groups 0 Constitutional isomers molecules that have the same chemical formula but different structures 0 Stereoisomers isomers than either have cistrans isomers or asymmetric centers 0 Terms to know 0 Chiralchiralitychiral center archival a molecule that has four different substituents around it or no plane of symmetry 0 Plane of symmetry an imaginary plane that can diVide a molecule and have one side mirror the other 0 Asymmetric Center an atoms with sp3 bonds and four different r groups 0 Enantiomers two compounds that are chiral isomers of each other re ections of each other They have the same physical and chemical properties but can react differently from each other
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