lecture 5 - CHEM 231 How functional groups change...

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Unformatted text preview: CHEM 231 How functional groups change properties of organic compounds LECTURE 5 LECTURE 5 1 Introduction to functional groups It is best to learn the functional groups early We will start with simple `heteroatom' functional groups and move to more complex functional groups Since we have already looked at halogens in alkane nomenclature we will start with them as functional groups Lecture 5 2 Halogens The halogens: F, Cl Br, I can make one bond in organic chemistry The bonds made between C and halogens are polarized H3C F Methyl fluoride Lecture 5 3 Halogens The bond made between C and F is very short Fluorine bucks the trend of other halogens it is important to note the CF bond isnot a reactive bond Unlike other halogens, the inclusion of fluorine in a compound tends to reduce the bp Alkyl halides with multiple fliuorines are not very soluble in other organic cpmpounds Lecture 5 4 The other Halogens. Cl, Br and I The bonds made between C and other halogens are progressively longer as the halogen size increases As the bond between carbon and halogens gets longer, the reactivity increases `longer bonds are more reactive bonds' H2 Cl I CH3 C H2 H2C Br CH CH C H3C C CH3 CH2 H2 I H3C CH2 2chloropentane 1bromo2methylbutane 1,2diiodoethan Lecture 5 5 Introduction to functional groups In the case of chlorine, bromine and iodine the density greatly increases, with each halogen added Boiling point increases with added halogen. Lecture 5 6 Pnictides and chalcogens Pnictides , N and P and chalcogens O and S are elemental functional groups These elements have lone pairs and can have multiple bonds The bonds that N and O make to carbon are short and are not very reactive Since P and S are third row elements they have longer bonds and these bonds can be broken easily Lecture 5 7 Pnictides and chalcogens Pnictides , N and P and chalcogens O and S are elemental functional groups The key features are the lone pairs and ability to have multiple bonds The lone pairs allow these elements to behave as Lewis bases The greater electronegativity of these elementsmake compounds containing NH; OH; PH and SH bonds much more acidic than CH bonds Since NH; OH; PH and SH combine lone pairs and a bond to hydrogen, intermolecular hydrogen bonds can form Lecture 5 8 Pnictides and chalcogens Pnictides , N and P and chalcogens O and S are elemental functional groups A key feature of N, O,P and S are the lone pairs and Since NH; OH; PH and SH combine lone pairs and a bond to hydrogen, intermolecular hydrogen bonds can form Hydrogen bonding is responsible for the unusally high boiling points of water and alcohols. Lecture 5 9 Common FG with nitrogen oxygen Pnictides , N and P and chalcogens O and S are elemental functional groups A key feature of N, O,P and S are the lone pairs and Since NH; OH; PH and SH combine lone pairs and a bond to hydrogen, intermolecular hydrogen bonds can form Hydrogen bonding is responsible for the unusally high boiling points of water and alcohols. Lecture 5 10 The vinyl group The vinyl group is a 2carbon fragment that is an alkene When this fragment is a functional group we refer to it as vinyl instead of the more formal ethenyl Vinyl chloride is probably the most important of the vinyl compounds It is used to make polyvinyl chloride (PVC) Cl HC CH2 HC CH2 Vinyl chloride Lecture 5 11 The allyl group This is a 3carbon fragment is important in organic chemistry because allylic cations anions and radicals are especially stabilized They are especially stabilized by resonance Lecture 5 12 The phenyl group Phenyl is the name that is used for a benzene ring when it is a group Phenyl groups are incredibly common in nature Lecture 5 13 The phenyl group Lecture 5 14 The benzyl group The benzyl group is a 7 carbon fragment that is very similar in reactivity and stability to the ally group. Benzyl cations, anions and radicals are also well stabilized through resonance. Lecture 5 15 The alkynyl group An alkyne as a substituent is called an alkynyl group. We will learn a number of reactions of alkynyl groups later in the semester Lecture 5 16 The carbonyl group is a polar unit common to a number of FG These include aldehydes and ketones O H3C H H3C O CH3 The carbonyl as part of a functional group Lecture 5 17 Ketones and aldehydes are very reactive The carbonyl as part of a functional group O H3C Nucleophiles add here Electrophiles add here CH3 Lecture 5 18 The carbonyl as part of a functional group They also include the carboxylic acid derivatives O H3C O H3C OH H3C Cl O NH2 H3C H3C O O O O O Lecture 5 19 The carbonyl as part of a functional group They also include the carboxylic acid derivatives O H3C O H3C OH H3C Cl O NH2 H3C H3C O O O O O Lecture 5 20 The nitrile is related to the carboxylic acid Nitriles or cyano are polar and reactive groups N C H N C CH3 N C N C Na Lecture 5 21 Sulfonic acid group Sulfonic acid groups are highly soluble I polar solvents and are useful as leaving groups in substitution chemistry O O CH3 O O H3C S HO R H3C C O S CH 3 H3C H3C O C CH3 + O S O CH3 O O S O CH3 O O S O CH3 The sulfonate anion is very well stabilized by resonance Lecture 5 22 Nitro groups are common in aromatic chemistry. The formal + charge on nitrogen makes the group very electron withdrawing. We will see the results of this electron withdrawing nature later in the course. The nitro group Lecture 5 23 The nitro group O N O O O N CH3 O N O O2N O CH3 NO2 O N These are 2 representations of a famous nitro compound Lecture 5 24 O N O NO2 title Lecture 5 25 ...
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This note was uploaded on 10/06/2008 for the course CHEM 231 taught by Professor Kissling during the Spring '08 term at Binghamton.

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