materi-stereokimia-2007
DESCRIPTION
stereokimiaTRANSCRIPT
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MATERI KULIAH KIMIA ORGANIK II
SMT IV 3 SKS
BAB I. STEREO KIMIA
BAB II. SENYAWA BERGUGUS FUNGSI JAMAK
BAB III. KARBOHIDRAT
BAB IV. ASAM AMINO, PEPTIDA, DAN PROTEIN
BAB V. LEMAK
BAB VI. HIDROKARBON AROMATIK POLISIKLIK
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1. Buku Teks Kimia Organik II (Matsjeh, S., et.al.,
1996, Kimia Organik II,
Departemen Pendidikan dan Kebudayaan
DIKTI)
2. Fessenden, R.J., and J S Fessenden, 1997,
Kimia Organik, Alih Bahasa
A.H Pudjaatmaja, Jilid 1, Edisi ketiga, Jakarta:
Erlangga
3. Paul R Young, 2000, Organic Chemistry On
Line, University Illinois
Chicago
4. Solomons, 2000, Organic Chemistry, 6th
edition, Wiley and Sons
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SOME ADVICE ON STUDYING FOR ORGANIC CHEMISTRY
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missingmaterial
STRUCTURE OF KNOWLEDGE IN ORGANIC CHEMISTRYSTRUCTURE OF KNOWLEDGE IN ORGANIC CHEMISTRY
Builds like a pyramid balancedon its point.
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The whole structurecollapses !!!
If something is missing …..
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STUDY TO UNDERSTAND THE MATERIAL
ANYTHING THAT YOU DO NOT MASTER WILLCOME BACK TO HAUNT YOU LATER
You literally cannot forget anything in this course.
The material keeps building on itself.
WE WILL BUILD ON EARLIER TOPICS TO DEVELOP NEW ONES
MATERIAL IN THIS COURSE IS CUMULATIVEMATERIAL IN THIS COURSE IS CUMULATIVE
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IF YOU DON’T UNDERSTAND SOMETHING….. GET HELP AS SOON AS YOU CAN
See me after class, during office hours, or makean appointment.
DO AS MANY PROBLEMS AS YOU CAN FINDTIME FOR IN YOUR SCHEDULE
Doing problems really cements your understandingit requires you to apply what you learn.
THE END-OF-CHAPTER PROBLEMS ARE THE MOST HELPFUL
Active learning is more effective than passive study.
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6 LANGKAH PENTING UNTUK SUKSES KIMIA ORGANIK
1) berada di kelas;
2) bertanya di kelas (jika menemui kesulitan)
3) Take good notes = buat catatan yang baik
persiapan dengan membaca materi sebelum
masuk kelas, setelah kuliah: baca lagi,
buat Ringkasan dan tulis kembali
4) Kerjakan PR pada waktunya
5) Practice, practice, practice!
6) Pelajari bagaimana ujian dengan baik
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We retain : 90% of what we say as we do a thing
70% of what we say as we talk
50% of what we see and hear
30% of what we see
20% of what we hear
10% of what we read
….. a psychological study
STRANGE BUT TRUESTRANGE BUT TRUE
ACTIVE
PASSIVE
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STEREO KIMIA
Studi mengenai molekul-molekul dalam ruang 3 dimensi
Bagaimana atom-atom dalam suatu molekul ditata dalam
ruangan satu relatif yang lain
1. ISOMER GEOMETRI
Ketegaran (rigidity) dalam molekul dapat mengakibatkan
isomer
2. KONFORMASI MOLEKUL
bentuk molekul dan bagaimana bentuk ini bisa berubah
3. KIRALITAS MOLEKUL
Bagaimana penataan kiri atau kanan atom-atom disekitar
atom C dapat mengakibatkan isomer
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Pusat stereo; titik dalam suatu molekul yang menghasilkan stereoisomer
jumlah stereoisomer yang mungkin adalah = 2n , n pusat stereo
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Pusat Khiral – ‘‘chirogenic centre’ = ‘pusat yang menghasilkan senyawa khiral
• Pusat khiral = pusat asimetrik ; mengikat 4 atom/gugus berbeda
A and B = enantiomers (‘optical isomers’)! – Pusat khiral
CCH3Br
H3CH2C
H
*
A
CCH3CH2CH3
Br
H
*
B
• Enantiomer adalah khiral! – • senyawa khiral tidak berimpit dengan bayangan
cerminnya.
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Why is chirality important?Chiral species fits in chiral binding site (matched key and lock)
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Chiral species does not fit in binding site (mismatched key and lock)
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Loius Pasteur
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isomers adalah senyawa berbeda yang memiliki rumus molekul
sama, contoh C4H8:
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Ada perbedaan letak gugus-gugus/atom-atom
1. Dilihat prioritas substituen yang terikat langsung ke C ikatan rangkap;Nomor atom tertinggi memperoleh prioritas tertinggi
Contoh; H– < C– < N– < O– < Cl–. (untuk isotop; prioritas sesuai dengan namor massa)
2. Jika atom yang terikat langsung ke ikatan rangkap
sama; maka lihat atom berikutnya. Contoh;
CH3– < C2H5– < ClCH2– < BrCH2 < CH3O–
Stereoisomer Alkena; Stereoisomer Alkena; Isomer GeometriIsomer Geometri,,
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3. Jika 2 gugus prioritas tertinggi terletak pada satu
sisi = cis
Jika 2 gugus prioritas tertinggi terletak pd sisi
berlawanan = trans
4. bila ke empat gugus atau atom yang terikat ke
atom C ikatan rangkap berbeda; maka dipakai
penamaan E (= entgegen) & Z (=zusammen),
Z equivalent ke cis dan E equivalent ke trans.
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Sistem E dan Z
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ISOMER GEOMETRI PADA SENYAWA SIKLIK
H H
H
H H
H H
H
H
H
CH3
OH
Di atas bidang;Gugus terikat pada ujung-atas garis vertikal
Di bawah bidang;Gugus terikat pada Ujung-bawah garis vertikal
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Contoh:
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Konformasi Senyawa Rantai Terbuka
Gugus-gugus yang terikat oleh ikatan
sigma dapat berotasi mengelilingi ikatan,
Dapat memiliki tak terhingga banyak posisi
didalam ruang relatif satu terhadap yang
lain
Menggunakan Proyeksi Newman
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Hanya ada 1 ikatan C-C, struktur rotasi (rotamer) yang ada:
staggered dan eclipsed.
Nama Konforme r
Wedge-Hatched Bond Structure
SawhorseStructure
Newman Projection
Bond Repulsions in Ethane
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Profil Energi Potensial untuk Konformer Etana
Dihedral Angle
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Profil Energi Potensial untuk Konformer Butana
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Aspek penting dari Stereoisomer Konformasi:
1.Interkonfersi konformasi dalam molekul sederhana terjadi cepat pada temperatur kamar, isolasi konformer murni biasanya tidak mungkin.
2. Konformer spesifik membutuhkan tatanama khusus, seperti staggered, eclipsed, gauche dan anti
3. Konformer spesifik tersusun dari sudut dihedral.
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4. konformasi Staggered sekitar ikatan tunggal
C-C lebih stabil (punya energi potensial
terendah) dibandingkan konformasi eklips.
5. Konformer Gauche pada butana kurang
stabil dari pada konformer anti sekitar 0,9
Kkal/mol. Nilai ini disebabkan rapatnya 2
gugus metil (steric hindrance) pada struktur
Gauche
6. Konformer Butana B dan C memiliki struktur
bayangan cermin yang tidak identik, sudut
dihedral 2400 & 3000.
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Bentuk Senyawa SiklikBentuk Senyawa Siklik
600 900 1080 1200
Sudut ikatan menurut BAEYER
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Diagram proyeksiMenggambarkan struktur 3 dimensi
ke 2 dimensi :
Proyeksi Fischer Proyeksi Newman
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Proyeksi FISCHER
Vertikal; menjauhi pembaca
Horizontal; mendekati pembaca
Proyeksi Fischer bisa berotasi dan dimanipulasi
Rotasi 900 tidak dibolehkan; karena menghasilkan
enantiomer awal.
Rotasi 1800 menghasilkan konfigurasi identik, rotasi
2700 menghasilkan enantiomer
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Aturan Penataan ulang proyeksi Fischer :
1. merubah 2 gugus pd proyeksi Fischer; menghasilkan
enantiomer dari senyawa awal
2. perubahan gugus 2 kali menghasilkan stereokimia awal
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Proyeksi Fischer dengan 2 C khiral
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Urutan penataan ke 4 gugus di sekitar atom khiral
Tata nama R, S
(R = Rektus = ke kanan ; S = Sinister = Kiri)
(R)-alanine
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1. Urutkan ke 4 gugus (berdasarkan prioritasnya)
Berdasarkan no atom; dari yg terikat langsung
pada C kiral
b. Bila atom yang terikat langsung pada C khiral sama;
maka prioritas ditentukan oleh atom berikutnya
c. Ikatan rangkap 2 dianggap mengikat 2 atom
yang sama
d. Ikatan rangkap 3 dianggap mengikat 3 atom
yang sama
e. Atom yang mengikat 2 C yang riel punya prioritas lebih
tinggi dari pada C dengan ikatan rangkap
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2. Isotop dengan massa lebih besar memperoleh
prioritas lebih tinggi
3. Proyeksikan molekul sehingga ggs prioritas
terendah berada di belakang
4. Tarik suatu anak panah dari gugus prioritas
tertinggi ke terendah
Jika searah dengan putaran jarum jam = R
Jika berlawanan dengan putaran jarum jam = S
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Urutan prioritas: Cl (tertinggi) > C-C > C-H > H.
Sehingga (R)-2-khlorobutana
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(S)-2-bromo-butane
C
CH3
Br
H3CH2C
H*a
b
c
dCCH3Br
H3CH2C
H
*C
CH3
Br
H3CH2C
H*
a
b
c
d
CCH3CH2CH3
Br
H
* C
CH3
CH2CH3
Br
H*
ab
cd
C
CH3
CH2CH3
Br
H
*a b
c
d
(R)-2-bromo-butane
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CH Br
CH3CH2O
CH3
* CH Br
CH3CH2O
CH3
* ab
cd CCH3CH2O
Br
CH3
H
* abc
d
(R)-(1-bromoethyl) ethyl ether
C
CH3CH2O
Br
CH3
H *a
b
c
d
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CH3CH2CH
OH
CH3
*CH3CH2C
H
OH
CH3
*
a
b
c
d
C
CH2CH3
H
OH
CH3
*
a
b
cd
C
CH2CH3H
OH
CH3
*
a
bc
d
(R)-2-butanol
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• Gambarkan struktur dari (S)-1-kloro-2-butanol !
C *
a
b cd
Posisi struktur : ClCH2C*H(OH)CH2CH3
Perioritas : HO- = a, ClCH2- = b, CH3CH2- = c, H- = d
(S)-
CCH2CH3H
OH
ClCH2
*1 2 3 4
Pusat khiral (C*) pada C2: gugus yang terikat ke C* : HO- , ClCH2-, CH3CH2-, H- .
Contoh
CCH2CH3H
OH
ClCH2
*
a
b cd
1 2 3 4
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Berikan stereostruktur dari (R)-2-iodopentana !
C *
a
c bd
(R)- 2-iodopentana: CH3C*H(I)CH2CH2CH3; Pusat khiral (C*) di C2 Gugus pada C* : I- , CH3-, CH3CH2CH2, H- .
CCH2CH2CH3H
I
CH3
*
a
bcd
1 2 3 4 5
(R)- 2-iodopentana
Prioritas: I- = a, CH3CH2CH2- = b, CH3- = c, H- = d
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Senyawa C – dua pusat khiral…..(2RR,3SS)-2,3-dibromobutane
… is it non-superimposable upon its mirror image?
Lihat C dan cerminnya D :
C and D identical!
(2RR)
C
H
C
CH3 Br
CH3
HBr
**
CC
H
C
CH3 Br
CH3
HBr*
a
b
cd
1
2C
H
C
CH3 Br
CH3
HBr
*
a
b
c d
34(3SS)
Tetapi…apa C senyawa khiral ?
C
H
C
Br CH3
BrH
CH3
**
23
D
1
4
C
H
C
CH3 Br
CH3
HBr
**
23
C
1
4
(2RR)
(3SS)
(2SS)
(3RR)
(2RR,3SS)- or meso-2,3-dibromobutane
-Bidang cermin atau bidang simetri
C
H
C
Br CH3
BrH
CH3**
D
1
2 Pusat Khiral
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Senyawa Meso: setiap pusat khiral dihubungkan dengan gugus yang sama dalam bidang cermin
C
H
C
OH
OHH
COOH
COOH
**
1
23 4
(2RR,3SS)- or meso-2,3-dihydroxybutanedioic acid
ormeso-tartaric acid
m.p. 140 °C
(1RR,2SS)-1,2-dibromo-cyclobutane
HH
BrBr
**
(2RR,3SS)- or meso-2,3-dibromobutane
C
H
C
CH3 Br
CH3
HBr
**
23
1
4
(2RR,3SS)-2-bromo-3-klorobutana
C
H
C
CH3 Cl
CH3
HBr
**
23
1
4
Bukan senyawa meso!
Lanjutan ….
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diastereoisomers!• Relationship between C and E or C and F:
• E,F not superimposable – both chiral- enantiomersenantiomers!
C
H
C
Br CH3
CH3
HBr
**
E
23
1
4
Compounds C, E and F
C
H
C
CH3 Br
BrH
CH3**
23
F
1
4
(2RR)
(3RR)(2SS)
(3SS)
• Stereoisomers which are not enantiomers are diastereoisomers or diastereomers.
C
H
COH
HCOOH
OHHOOC
**
(2RR,3R R )- 2,3-dihydroxybutanedioic acid
or(2RR,3RR)- tartaric acid
m.p. 170 °C
C
H
C
CH3 Br
CH3
HBr
**
23
C
1
4
(2RR)
(3SS)
C
H
C
OH
OHH
COOH
COOH
**
1
23 4
(2RR,3SS)- or meso-2,3-dihydroxybutanedioic acid
ormeso-tartaric acid
m.p. 140 °C
Diastereoisomer
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Identical m.p., b.p., differ in specific rotation: Solution irradiated with plane polarized light; = 589 nm (sodium ‘D’ emission line) in polarimeter.
rotation ° ‘to the right’ – ‘dextrorotatory’ d- or (+); ‘to the left’ – ‘levorotatory’ l or (-).
specific rotation []589 = .100/c.l c = conc. g./100mLl = length of sample tube (dm)
• Optically active compound: displays optical rotation - pure enantiomer, or mixture of enantiomers containing more
than 50% of one enantiomer.• Racemic mixture: mixture contains 50% of each enantiomer, = 0°. • Racemate or racemic ‘compound’ (rac): crystalline or pure liquid 1:1 mixture of enantiomers
Properties of Enantiomers
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C
H
C
OH
HOH
COOH
HOOC**
m.p. 170 °C
[]D = +12.4°
(2SS,3SS)-(-)- tartaric acid
[]D = -12.4°
rac- or (2RSRS,3RSRS)- tartaric acid
or(±)- tartaric acid
[]D = 0°
[]D = 0°
Racemate
m.p. 210 °C
-crystals consist of 1:1 mixture of enantiomers
Examples
C
H
C
OH
OHH
COOH
COOH
**
1
23 4
(2RR,3SS)- or meso--tartaric acid
m.p. 140 °C
C
H
COH
HCOOH
OHHOOC
**
(2RR,3RR)- (+)-tartaric acid
m.p. 170 °C
Properties of Enantiomers (cont.)