lesson 14 acidic and basic character of organic compounds

8/16/2019 Lesson 14 Acidic and Basic Character of Organic Compounds

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Lesson 14

ACIDIC AND BASIC CHARACTER

OF

ORGANIC COMPOUNDS


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Acidity Measurements

•The acidit constant! K a! "eas#$es the e%tent to &hich a B$'nst$ans(e$s a )$oton to &ate$

*A + *H,O-+

K a . ///// and )K a . 0o K a

*HA+

•Re0ati2e acidities a$e "o$e con2enient0 )$esented on a 0oa$it)3a!

2


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)3a a0#es (o$ T)ica0 OH Co")o#nds

3


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ACIDIT5 OF ALCOHOLS! PHENOL AND CARBO65LIC

Brønsted-Lowry defnition o acid

•An acid is a )$oton dono$

4

Note7 a )$oton is a hd$oen ion 8H-9

An acid in solution sets up this equilibrium:

hd$o%oni#"


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STRENGTHS OF :EA3 ACIDS

•The strengths of weak acids are measured on the )3a scale. The sm

number on this scale, the stronger the acid is.

5

Ethanoicacid

4.76

Phenol 10.00

ethanol about 16

Inc$easinAcidit

Ethano0 is so &ea; &ith a )3a o( a


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• Resonance sta


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• The dotted 0ine $e)$esents the de0oca0isation@ The neati2e cha$

cent$a00 on that end o( the "o0ec#0e to sho& that it isnt 0oca0isthe o%en ato"s@

• The "o$e o# can s)$ead cha$e a$o#nd! the "o$e sta


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• Etho%ide! the con#ate


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10

Ind#cti2e E((ect 7"nducti#e effect is defined as $ermanent dis$la

of shared electron $air in a carbon chain towar

electronegati#e atom or grou$.


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T)es o( Ind#cti2e e((ect 7

1@Neati2e Ind#cti2e E((ect 7

8/I e((ect! E0ect$on &ithd$a&in e((ect9when an electronegati#e atom or grou$%more electronegati#hydrogen& is attached to the terminal of the carbon chain in

com$ound, the electrons are dis$laced in the direction of the

atom or grou$.

!'(2 ) !*' ) !*((+ ) ) *l ) -r ) " ) (+ ) *+5) +


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@ Positi2e Ind#cti2e e((ect 78-I e((ect! E0ect$on $e0easin e((ect9/hen an electro$ositi#e atom or grou$ %more electro

than hydrogen& is attached to the terminal of the carin a com$ound, the electrons are dis$laced away fro

attached atom or grou$.

%*+3&3*! ) %*+3&2*+! ) !*2+5 ) ! *+3.


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Ind#cti2e e((ect is #se(#0 in e%)0ainin the st$enth o( so"e o$anic acids

a9 E((ect o( s#


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INDUCTIE EFFECTS

• E0ect$on&ithd$a&in $o#)s "a;e an a0coho0 a st$one$ acid sta


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THE INDUCTIE EFFECT IN ALIPHATIC CARBO65LIC ACIDS


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Acidit inc$eases

D#e to sta


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Basic cha$acte$ o( a0i)hatic a"ines! a"ides and a$o"ati

)3<a"ides

≈

1J

Phen0a"ine8ani0ine98an a$o"atic a"ine9

C=HJNH K@4

a""onia NH,

4@

"eth0a"ine CH,NH ,@4

eth0a"ine CH,CHNH ,@

Basicitinc$ease

A0i)hatica"ines 1b base dissociation constant

$1b !log01b


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Fo$ a0i)hatic a"ines!


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• A$o"atic a"ines8e@@ )hen0a"ine! )3


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BASICIT5 OF AMIDES


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BASICIT5 OF AMIDES

A"ides a$e e%t$e"e0 &ea; acids and a0so 2e$ &ea;


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A"ides a$e NOT


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A"ino acids contain (#nctiona0 $o#)s

The a00 ha2e a si"i0a$ st$#ct#$e the identit o( R1 and R 2a$

Q:ITTERIONS


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Q:ITTERIONS

• a witterion is a di)o0a$ ion it has a )0#s and a "in#s cha$e in its structure• a $roton from the *((+ grou$ mo#es to '+2

• amino acids eist as ?&itte$ions at a certain $+• the $+ #alue is called the isoe0ect$ic )oint• $roduces increased inter!molecular forces

• melting and boiling $oints are higher

A zwitterion is a compound with nooverall electrical charge, but whichcontains separate parts which arepositively and negatively charged.

Acid


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• amino acids $ossess acidic and basic $ro$erties due to

functional grou$s

• they will form salts when treated with acids or alkalis.

Acid


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PROTEINS


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PROTEINS

Ne#t$a0 a"ino acids


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Ne#t$a0 a"ino acids

I( the R $o#) does not contain an acidic $o#)s! the a"ino acid is ne#t$a0

Acidic a"ino acids

I( the R $o#) has "o$e acidic $o#)s then the a"ino acid is acid


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Basic a"ino acids

I( the R $o#) has "o$e

lesson 14 acidic and basic character of organic compounds

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