2120 ME 1 – Chemistry – Flashcards

-Carbon forms strong covalent bonds to other carbons and to other elements such as hydrogen, oxygen, nitrogen, and Sulfur

*1.5billion known inorganic compounds

*7billion known organic compounds

-molecular formulas tell the NUMBER of different atoms present in the molecule (C2H2, etc)

-structural formula show the connection between different atoms present in the molecule

** types are dot structure, dash formula, and condensed formula

-dot formulas are more cumbersome to draw than dash formulas and condensed formulas

-lone-pair electrons are often (but not always) drawn in, especially when they are curcial to the chemistry being discussed

-Each dash represents a pair of electrons

-this type of representation is meant to emphasize connectivity and down not represent the 3-dimensional nature of the molecule (appear to have 90 degree angles for carbon, even though it is tetrahedral and angles in reality are 109.5)

***there is relatively free rotation around single bonds, so dash formulas with single bonds can be equivalent**

so long as connectivity does not change

*constitutional isomers have the same molecular formula, but different connectivity

-in these representations, some or all of the dash lines are omitted

-in partially condensed structures all hydrogens attached to an atom are simply written after it but some or all of the other bonds are explicitly shown

-in fully condensed structure all bonds are omitted and atoms attached to arbon are written immediately after it 

-for emphasis, branching groups are often writted using vertical lines to connect them to the main chain.

-a further simplification of drawing organic molecules is to completely omit all carbons and hydrogens and only show heteratoms (O,Cl,N etc) explicitly

-each intersection or end of line in a zig zag represents a carbon with the appropriate amount of hydrogens

-cyclic compounds are condensed using a drawing of he corresponding polygon

-multiple bonds are indicated by using the appropriate number of lines connecting the atoms

-the most important factor in determining the shape of a organic molecule is the shape of the carbon center

-the different bonding modes around each C are: four simple bonds, two single bonds and one double bond, or one single and one triple bond

-Using VSEPR theory, the corresponding shape of each carbon center is, respectively: tetrahedral, trigonal planar, and linear

-trigonal planar arrangements of atoms can be drawn in 3D in teh plane of the paper 

-bond angles should be approx 120 degrees

- these can also be drawn side on with the central bond in the plane of the paper, one bond forward, and one bond back

-generally to represent a tetrahedral atom:

-two of the bonds are drawn in the plane of the paper about 109 degrees apart

-the other two bonds are drawn in the opposite direction to the in-plane bonds but right next to each other

-hydrocarbons contain only carbon adn hydrogen atoms

-subgroups: 

alkanes - contain only C-C single bonds

alkenes - contain one or more C-C double bonds

alkynes - contain one or more C-C triple bonds

-aromatic hydrocarbons contain benzene-like stable structure

saturated hydrocarbons - contain only C-C single bonds

unsaturated hydrocarbons - contain double or triple C-C bonds (alkenes, alkynes, aromatics)

-contain fewer than maximum number of hydrogens per carbon

-capable of reacting with H2 to become saturated

 ALKANES

 -principle sources of alkanes are natural gas and petroleum

-smaller alkanes (C1-C4) are gases at room temperature

METHANE

-a major component of the atmosphere of many planets

-major componenet of natural gas

-produced by primitive organisms called methanogens found in mud, sewage, and bodies

-methane is moredirectly related to food production and population growth so it could also dominate in the near future

-frozen methane is also found in the Arctic Ice Caps and will be released due to global warming thus exacerbating the problem

-this is far more serious than people realize

ALKENES

-ethene (ethylene) is a major industrial feedstock

-used in the production of ethanol, ethylese oxide and the polymer polyethylene

-propene (propylene) is also very important in industry

-molecular formula is C3H6

-used to make the polymer polypropylene and is the starting materil for acetone

 *** in a molecule, 2 double bonds side by side are very unlikely**

-many alkenes occur naturally 

TURPENTINE

-An organic solvent and synthetic material

-turpentine has been used medically since ancient times

-a highly effective treatment for lice

-when mixed with animal fat is a primitive chest rub for nasal and throat ailments

-drinking turpentine is extremely dangerous and can be life threatenign. In addition, drinking turpentine is not an effective way to induce an abortion.

ALKYNES

-many alkynes are of biological interest

-capillin is an antifungal agent found naturally

-dactylyne is a marine natural product

-ethinyl estradiol is a synthetic estrogen used in oral contraceptives

conjugated  - double bond every two carbons alternating

isolated dbl bond - in haphazard areas (less stable)

cumulated dbl bond - consecutive dbl bonds (very unstable)

-benzene is the prototypical aromatic compound (nice smell)

-the kekule structure (named after August Kekule) is a six membered ring with alternating double and single bonds

-Benzene does not actually have discreet single and double C-C bonds

-all C-C bonds are exactly equal in length (1.38A)

-This is b/w the length of a carbon-carbon single bond and a C-C double bond

-Resonance Theory explains this by suggesting there are two resonance hybrids that contribute equally tothe real structure

-the real structure is often depicted as a hexagon with a circle in the middle.

#C/MF/NAME

1/CH4/methane

2/C2H6/ethane

3/C3H8/propane

4/C4H10/butane

5/C5H12/pentane

6/C6H14/hexane

7/heptane

8/octane

9/nonane

10/decane

11/undane

General Formula: C_nH_2n+2

-For acyclic saturated hydrocarbons, use the ending suffix -ane

-linear alkanes named according to their chain length

-from branched alkanes, find longest continuout chain, and name branch before naming main chain

**groups attached tot he chain are called substituents. Saturated hydrocarbon substituents are called alkyl groups (substitude -ane with -yl) 

1/CH3/methyl

2/CH5/ethyl.

etc

*****saturated hydrocarbon substituents are called alkyl groups******

*an alkyl group is "iso" (ie. isopropyl/isobutyl), if it contains 3+ carbons and has a fork at the end

-The main chain is numbered to give the first substituent the lowest number. In addition, if more than 1 identical group is attached to the chain, use prefix di, tri, or tetra.

-**if there are 2 or more different substituents, then list them alphabetically.

-Punctuation is important..

-hydrocarbons are written as 1 word

-use commas to separate numbers

-use hyphens to separate numbers and names

CLASSIFYING CARBONS

-carbon centers are classified as follows:

-Primary carbons are connected to only one other carbon (3H)

-Secondary carbons are connected to two other carbons (2H)

-Tertiary carbons are connected to three (1H)

-a benzene ring with a hydrogen removed is called a phenyl and can be represented in various ways (C₆H₅-- or Ph-- etc..)

Toluene (methylbenzene) with its methyl hydrogen removed is called a benzyl group (CH₅CH₂- or Bn-)

F - fluoro-

Cl - chloro-

Br - bromo-

I - iodo-

-name alphabetically if more than one..

-simple haloalkanes are commonly called Alkyl Halides

chloromethane = Methyl Chloride

bromomethane = Ethyl Bromide

2-fluoropropane = isopropylfluoride

dichloromethane = Methylene chloride

trichloromethane = chloroform

tetrachloromethane = carbon tetrachloride

-They are also callsified based on the carbon the halogen is attached to

-if the carbon is attached to one other carbon hat carbon is primary and the alkyl halide is also primary

-if the carbon is attached to two other carbons, that carbon is secondary and the alyl halide is also

-if three, then both are tertiary

HALOALKANES AS COMMON SOLVENT AND ANESTHETICS

-dry cleaners use CCl4 for grease removal

-CCl4 is toxic to liver and can cause cancer

-residual still in environment from 1920s

-today dry cleaners use other haloalkanes such as CH2Cl2, 1,1,1-trichloroethane, and FCl2C-CClF2

-CHCl3 was once used as an anesthetic but now we know that it is toxic and maybe carcinogenic

-CCl3F and CCl2F2, CFCs were widely used as propellants and refrigerants in home and car air conditioners

-CFCs catalyze the decomposition of ozone therefore thinning the ozone layer in the stratosphere

-one chlorine atom can destroy 100k ozone molecules

DBP= disinfection bi-product

-CFCs caused by disinfecting water

-the generat molecular formula is  C_nH_2n

-add cyclo in front of the alkane name

-the one with the most substituents will be #1 carbon

-go around the ring to give the lowest location number

-functional group families are charaterized by the presence of a certain arrancement of atoms calld a functional group

-a functional group is th site of most chemical reactivity of a molecule

-the functional group is responsible for many of the physical properties of a molecule

-Alkanes do not have a functional group (carbon-carbon single bonds and carbon-H bonds are generally very unreactive)

-alkane

-alkene

-alkyne

-aromatic

-haloalkane

-alcohols

-ethers

-amines

-aldehydes/keytones

-carboxylc acids

-esters

-amides

-nitriles

-in alcohols the hydrogen of the alkane is replaced by the hydroxyl (-OH) group

-an alcohol can be viewed as either a hydroxyl derivative of an alkane or an alkyl derivative of water

-alcohols are also classified according to the carbon the hydroxyl group is directly attahed to (2^o carbon means a 2^o hydroxyl)

-ethers have the general formula R-O-R or R-O-R' where R' is different from R

-these can be considered organic derivatives of water in which both hydrogens are replaced by organic groups

-the bond angle at oxygen is close to the tetrahedral angle

-amines are organic derivatives of ammonia

-they are classified according to how many alkyl groups replace the hydrogens of ammonia

-this is a different classification scheme than that used in alcohols

(formula is N)

RNHH - primary amine

RNR'H - secondary amine

RNR'R" - tertiary amine (3^o)

-Both contain the carbonyl group (C-O double bond)

-aldehydes have at least one carbon attached to the carbonyl group (RCHO) or (HCHO)

Ketones hav two organic groups attahed to the carbonyl group (RCOR or RCOR')

-all of these groups contain a carbonyl group bonded to an oxygen or nitrogen

;

-carboxylic acids contain the carboxyl (carbonyl + hydroxyl) group

RCOOH

-a carbonyl group is bonded to an alkoxyl (OR') group

 RCOOR'

-a carbonyl group is bonded to a nitrogen derived from ammonia or an amine

(RCON)

-an alkyl group is attached to a carbon triply bonded to a nitrogen

-this functional group is called a cyano group

(RCN)

-General Formula for Alkenes: CnH2n

-General Formula of Alkynes: CnH2n-2

;

-The main chain should contain the double (or triple) bond.

-It is numberd to give the double bond the lowest number. In addition, if the molecule has more than 1 double bond, use prefix di, tri, or tetra-ene (or yne)

;

-Cycloalkenes are numbered to give the double bond 1 and 2 and then the substituents the lowest number

-

-Isomers are different molecules with the same molecular formula

-many types of isomers exist

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**Isomers are divided into Constitutional Isomers (isomers whose atoms ahave a different connectivity) and Stereoisomers (isomers that have the same connectivity but that differ in the arrangement of their atoms in space)

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-Stereoisomers are further divided into Enantiomers (stereoisomers that are nonsuperimposable) and diastereomers (stereoisomers that are not mirror images of each other)

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*the # of consititutional isomers possible for a given molecular formula increases exponentially with the number of carbons

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*stereoisomers have same connectivity

-these are Cis-Trans stereoisomers

-if two identical groups occur on the same side of the double bond the compound is cis

-if they are on the opposite sides then the compound is trans

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**must be a double bond!! rotation is possible with a single bond!!

-When all substituents are different, it is difficult or ambiguous to determine the cis or trans designation

;

-Step 1 Determine the priority of A, B, C, D.

Step 22: If two higher priority groups are on the same side, it is ;Z; (cis). Otherwise, it is ;E; (trans).

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The Cahn-Ingold-Prelog system of determining priority...

1.priority is first assigned acording to atomic number. Small is low.

-the structure of methane with its four identical tetrahedral bonds cannot be adequately explained using the electronic configuration of carbon

-Hybridization of the valence orbitals (2s and 2p) provides four new identical orbitals which can be used for bonding in methane

;

-When one 2s orbital and three 2p orbitals are hybridized four new and identical sp³ orbitals are obtained

-when four orbitals are hybridized, four orbitals must result

-each new orbital has one part s character and 3 parts p character

-the four identical orbitals are oriented in a tetrahedral arrangement

-Orbital Hybridization is a mathematical combination of the 2s and 2p wave functions to obtain wave functions for the new atomic orbitals

;

LCAO treatment

-the four sp3 orbitals are then combined with teh 1s orbitals of four hydrogens to give the molecular orbitals of methane

-each new molecular orbital can accommodate 2 electrons

-the anti-bonding molecular orbitals are those not being used... empty... possible to access with color.. (absorbing light)

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DRAWING

-an sp3 orbital looks liek a p orbital with one lobe greatly extended (often the small lobe is not drawn)

-The extended sp3 lobe can then overlap well with the hydrogen 1s to form a strong bond

-the bond formed is called a sigma bond because it is circularly symmetrical in cross section when viewed along the bond axis

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ETHANE (C2H6)

-the carbo-carbon bond is made from overlap of two sp3 orbitals to form a sigma bond

-the molecule is approximately tetrahedral around each carbon

**generally there is relatively free rotation about sigma bonds

-very little energy is required to rotate around the C-C bond of ethane (13-26Cal/mol)

ETHENE

-The geometry around eah carbon is called trigonal planar

-all atoms sirectly connected to each carbon are in a plane (flat molecule)

-the bonds point towards the corners of a regular triangle

-bond angles are approx 120 degrees

;

-there are three sigma bonds around each carbon of ethene and these are formed by using sp2 hybridized orbitals

-the three sp2 hybridizd orbitals come from mixing one s and two p orbitals

-one p orbital is left unhybridized

-get 2sp² orbitals

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-the sp2 orbitals are arranged in a trigonal planar arrangement

- the remaining p orbital is perpendicular (orthoganol) to the plane

One sp2 orbital on each carbon overlaps to form a C-C sigma bond; the remaining sp2 orbitals for sigma bonds to hydrogen

-the leftover p orbitals on each carbon overlap to form a pi bond between the two carbons

-pi bonds are weaker than sigma bonds

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-the bonding pi orbital is lower in energy than the antibonding orbital

-in the ground state two spin paired electrons are in the bonding orbital

-the antibonding pi*orbital can be ocypied if an electron becomes promoted from a lower level (ie. by absorption of light)

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CHEMISTRY OF SUNSCREEN

-compounds used in sunscreen should posses at least these two properties:

1)minimal reaction on skin

2)UV light absorption

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RESTRICTED ROTATION

-there is a large energy barrier to rotation (about 264 KJ/mol)around the double bond

-this corresponds to the strength of a pi bond

-the rotational barrier of a carbon-carbon single bond is 13-26KJ/mol

-this rotational barrier results bcause the p orbitals must be well aligned for maximum overlap and formation of the pi bond

-retation of the p orbitals 90 degrees totally breaks the pi bond

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--Cis-Trans isomers are the result of restricted rotation about double bonds

-some cis-trans isomers differ markedly in their dipole moment

-the carbon in ethyne is sp hybridized

-one s and on p orbital are mixed to form two sp orbitals

-two p orbitals are left unhybridized

-the two sp orbitals are oriented 180 degrees relative to each other around the carbon nucleus

-the two p orbitals are perpendicular to the axis that passes through the center of the sp orbitals

-the sp orbitals on the 2 carbons overlap to form a sigma bond

-the remaining sp orbitals overlap with hydrogen 1s orbital

-the p orbitals on each carbon overlap to form two pi bonds

-the triple bond consists of one sigma and two pi bonds

Theyne has symmetrical pi bond

-Depictions of ethyne show that the electron density around the caron-carbon bond has circular symmetry

-even if rotation around the C-C bond occurred, a different compound would not result

-the C-C bond length is shorter as more bonds hold the carbons together

-with more electron density b/w the carbons, there is more "glue" to hold the nuclei of the carbons together-

-The carbon hydrogen bond lengths also get shorter with more s character of the bond

 -2s orbitals are held more closely to the nucleus than 2p orbitals

-a hybridized orbital with more percent s characteris held more closely to the nucleus than an orbital with less s character

-the sp orbital of ethyne has 50% s character and its C-H bond is shorter

-the sp3 orbital of ethane has only 25% s character and its C-H bond is longer

HOW DO YOU EXPLAIN THE EQUAL BOND LENGTHS IN BENZENE?

-All carbons in benzene are sp2 hybridized

-each carbon has a unhybridized p orbital

-there is a continuous overlap of p orbitals over the entire ring

-All 6 pi electrons are therefore delocalized over the entire ring and this results in the equivalence of all of the C-C bonds

-Ethane has relatively free rotation around the C-C bond

-such rotation leads to the formation of different conformers

-Ethane has TWO conformers***

-The staggered conformation has C-H bonds on adjacent carbons as far apart from each other as possible

-Newman projetion is a type of drawing that depicts the conformation of a specific conformer

For staggered ethane, say:

"the Dihedral (tortional) angle between these hydrogens (top/bottom) is 180 degrees)

-The exlipsed conformation has all C-H bonds on adjacent carbons directly on top of each other

-this version is more crowded and repulsion is stronger

****Very Unstable = High Energy****

-Use a potential energy diagram to conduct a Conformational Analysis

-staggered versions are generally more stable than eclipsed

 -ethane has 2 conformers

-butane has 6 important conformations (but only 4 are unique kinds)

*The stability of the different conformers is related to the repulsive van der Waals forces b/w the two methyls