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CHEM 2211: Test 1
functional groups
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groups of atoms within a molecule that have characteristic chemical behaviors.
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alkanes
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cmpds compsed of carbon atoms connected via c-c single bonds
also known as aliphatic cmpds
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hydrocarbons
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cmpds composed only of carbons and hydrogens
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saturated alkanes and hydrocarbons
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only contain c-c and
C-H single bonds. Max # of H's per carbon atom
CH3CH2CH3--> C3H8
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Methane
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CH4
1 C
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Ethane
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C2H6
2 carbons
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propane
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C3H8
3 carbons
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Butane
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C4H10
4 Cs
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Pentane
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C5H12
5 carbons
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Hexane
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C6H14
6 Cs
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Heptane
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C7H16
7 carbons
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Octane
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C8H18
8 carbons
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nonane
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C9H20
nine carbons
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decane
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C10H22
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straight chain alkanes
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cmpds that have carbons atoms connected in a single row
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branched chain alkanes
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exactly that they sound like-straight chains with branches
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isomers
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cmpds that have the same molecular formula but different structures.
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constitutional isomers
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cmpds that have the same numner and kind of atoms but differ in how the atoms are arranged (bonded)
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characteristics of constitutional isomers
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-different carbon skeletons
-diff. functional groups
-diff. funtional group location in the carbon chain
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alkane groups
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take away a H to make into alkyl groups
CH4 (Methane)--> -H = CH3 (Methyl)
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(Naming Alkanes) IUPAC
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International Union of Pure and Applied Chemistry
3 parts to IUPAC name
1. prefix
2. parent
3. suffix
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prefix
(alkanes)
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indicates where the substiuents are found
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parent
(alkanes)
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how many carbons are in the parent chain
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suffix
(alkanes)
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indicates what family/grouping the cmpd belongs to
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chemical properties of Alkanes
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-show little reactivity
-react with oxygen and halogens (Cl, Br, I...)
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physical properties of alkanes
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-as molecular weight increases so does the melting point and boiling point
-dispersion forces increase as molecular size increases
-MP and BP increase as well
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Phys Properties cont.
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increased branching lowers an alkanes boiling pt because :
-more spherical in nature than straight chains
-smaller surface area of contact (dispersion forces minimized)
-smaller dispersion forces overall
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stereochemistry (alkanes)
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systematic study of the 3D arrangement of atoms in a molecule
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conformations (alkanes)
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3D shape of a molecule at any given instant (assuming that rotation around single bond is frozen)
*they are at equilibrium at room temp
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conformers (alkanes)
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conformational isomers
-isomers that differ in the spatial orientation of thier atoms due to conformational changes (rotation of bonds)
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sawhorse representations
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-shows the molecule from an angle
-shows all C-C/ C-H bonds
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Newman projections
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-shows the molecule looking down a specific C-C bond
-shows all C-H bonds
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conformations of butane
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-anti (2 methyl groups are 180 degrees away from each other)
-gauche ( 2 methyl groups are 60 degrees apart)
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spectroscopy
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uses infrared light to identify functional groups
-interaction of electromagnetic energy with organic molecules
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frequency
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# of waves passed a fixed point per unit of time S-1 aka Hertz
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amplitude
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height of a wave
wavelength * freq. = speed
cm/s
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E
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amount of energy in one photon (quantum) of a given frequency
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exposure of an organic molecule to electromagnetic radiation:
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-absorption of E of certain wavelengths
-transmitted E of certain wavelenghts
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physical properties (cycloalkanes)
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-melting pts do not follow a set trend due to differing ring shapes that effect crystal formation
-Bps increase with molecular weight
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cylcoalkanes
physical properties
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less flexible than open chain alkanes
-alkanes have free rotation around the C-C single bond ( end to end sigma overlap)
-cannot fully rotate around thier C-C single bonds w/o breaking open the ring
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common ring sizes
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C3-C7 (are extremely restricted in thier flexibilty
-cannot fully rotate around their C-C bonds w/o breaking open the ring
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consequence of cycloalkane
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-has 2 sides
-tope face
-bottom face
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cycloalkane isomerization
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(cis-trans)
differ from constitutional isomers
-same order of atom connectivity
-differ in spatial arrangement of thier atoms
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stereoisomers
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cmpds that have thier atoms connected in the same order but differ in thier spatial arrangement (3D)
-cis ( same side)
-trans (accross)
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stablilty of cycloalkanes (Baeyer strain theory)
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-because carbon prefers to have bond angles of 109.5 degrees ring sizes other than 5 or 6 atoms may be too "strained" to exist
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nature of ring strain
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-rings larger than 3 atoms are not flat
-cyclic molecules can assume nonplanar conformations to minimize angle strain and torsional strain. "ring puckering"
-large rings have more attainable conformations then smaller ones
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angle strain
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expansion or compression of bond angles away from a stable 109.5 degress
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torsional strain
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eclipsing of bonds on neighboring atoms (e- repulsion)
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steric strain
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repulsive interactions b/w nonbonded atoms in close proximity
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cyclopropane
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-a three membered planar ring structure
-symmetrical ring w/ C-C-C bond angles of 60 degrees
-requires "bent" sp3 based C-C sigma bonds (weaker=more reactive)
-all of C-H bonds are fully eclipsed (torsional strain)
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bent bonds of cyclopropane
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-electron density of the C-C bond is displaced outward from the inter nuclear axis
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cyclobutane
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-has less angle strain than cyclopropane
-has more torsional strain
-slightly bent out of plane 1 carbon is 25 degrees above/below plane
-increasing angle strain but decreasing torsional strain
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cyclopentane
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-planar structure would have no angle strain but high amounts of torsional strain
-cyclopentane is nonplanar in order to reduce torsional strain
-four carbons are in plane while the fiffth atom is slightly ablove/below plane.
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conformations of cyclohexane
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-occur commonly/widely in nature
-free of angle strain and torsional strain
-most stable 3-D conformation has altering atoms in a common plane. optimal tetrahedral bond angles as achieved around each carbon atom
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axial and equatorial bonds pt 1
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a chair conformation has 2 types of substiuent positions:
-axial-->6 Hs perpindicular to ring
-equatorial-->6 Hs near the plane of the ring ( equator)
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axial and equatorial bonds pt 2
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-each carbon atom in cyclohexane has one axial and one equatorial hydrogen bond
-each face of a cyclohexane ring has 3 axial and 3 equatorial Hs (bonds)
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